2020 Silverado 6.6L Duramax 3500 HD Review

[92saturnsl2]

This hardly counts as a new car review but it's worth something. Drove this truck home (35 miles), co-worker owns it. He had a CEL code I pulled up on my scanner. It was related to injector timing, deviation, something to that effect. I'm too lazy to look up the exact code. I helped him diagnose it and some research lead me to a GM TSB that basically read like this (cliff notes): this code will not cause any driveability issues, but certain GM trucks in XXX vin range need ECU flashed to newest software. It was a smoking gun, fit the issue to a T.

So I traded him a welding table (in back of truck) and got free fuel going home and back to work (that's worth at least $15 to update the ECU to latest software. He pays for the SPS subscription.

Back to the truck review. I'm not sure I could call it pure work truck trim. It has the modern conveniences like touch screen radio / driver instrumentation display (full tire pressure readout), 3 camera views, blind spot detection, LED taillights, heated / power "leather" seats. But the hard plastics everywhere felt cheap and said to me that this is far from a deluxe model. Made to work but offer relative comfort to the driver; I think it does an okay job at that.

Ride is smooth as glass over small imperfections. Hit a road surface transition, pothole, frost heave, etc. and it's quite jarring, putting it mildly.

The engine/trans combo is what has me stumped. I don't drive light/medium duty diesels everyday but I'm a blue collar worker and have driven plenty of them. This is easily the most latel model diesel I've driven, most of my experience comes from pre-2010 diesels from the big-3. I remember back when the Ford 6.0L Powerstroke w/ 5sp auto came out and that thing would put you back in your seat and hold you there as long as your foot was in it. Same with that era Cummins / Duramax. The 10 speed in this model seems to mess it all up. Stomp on it from a stop and naturally the traction control kicks in real quick due to tires wanting to spin, but once you're at 20-30+ and actually accelerating, you get a very noticeable pause at each gear change (which come quick and often) which sort of ruins the experience. So for the first few moments it feels semi quick, but then the climb to 60-80 feels nothing like what I'm used to with the older trucks. However butt dyno testing can be wildly innacurate .

I'm sure some of you are thinking "this isn't made to be quick" and you'd be right. I know it can pull, he routinely hauls 20,000#+ with it. I still had fun seeing what it could do and was left underwhelmed given the specs. Played with the exhaust brake and while it might be more handy pulling a trailer, it didn't seem all that useful with the truck unloaded other than making some extra noise. In normal driving it was extremely quiet and transmission shifted smoothly. I was never a fan of the exterior design on these, but I think I'm warming up to it.

 

[BrendanC]

dad has an 800whp 2005 LLY. i have driven a 2020+ with the 10 speed and would side with the 10 speed every day of the week. it isn’t about putting you in your seat it’s about keeping the motor at peak torque for as long as possible. when you hook up to a trailer and get into it you’ll understand.

 

[21_6.7f450]

My F450 was getting beat by loaded dump trucks up to about 30mph and then it defueled between shifts up from there.
Tuning the trans took that out, drives like a completely different truck.

 

[92saturnsl2]

dad has an 800whp 2005 LLY. i have driven a 2020+ with the 10 speed and would side with the 10 speed every day of the week. it isn’t about putting you in your seat it’s about keeping the motor at peak torque for as long as possible. when you hook up to a trailer and get into it you’ll understand.

Absolutely-- hauling heavy loads with a 10 speed is probably night and day over the old 4-6 speeds in circa 2000-2010+ trucks. I still wonder if a 10 speed is necessary. Indirectly, pulling loads needs horsepower which is nothing but a math equation. These small diesels excel between 1600-2400. That can be covered with a 6-8 speed easily. I feel the 10 speed in these types of trucks are more for fuel economy. Grandpa and Mr. "needs a diesel truck" can commute at 1200-1500rpm all day long regardless of speed, yet the same truck pulling loads has those extra gear ratios that will keep it in the max powerband.

But definitely some electronic nannying going on in these new ones that keep torque in line for the driving conditions. Hopefully folks aren't buying these trucks for the type of acceleration experiments I was doing. Take my powertrain "review" with a grain of salt.

 

[BrendanC]

Absolutely-- hauling heavy loads with a 10 speed is probably night and day over the old 4-6 speeds in circa 2000-2010+ trucks. I still wonder if a 10 speed is necessary. Indirectly, pulling loads needs horsepower which is nothing but a math equation. These small diesels excel between 1600-2400. That can probably be covered with a 6-8 speed. I feel the 10 speed in these types of trucks are more for fuel economy. Grandpa and Mr. "needs a diesel truck" can commute at 1200-1500rpm all day long regardless of speed, yet the same truck pulling loads has those extra gear ratios that will keep it in the max powerband.

But definitely some electronic nannying going on in these new ones that keep torque in line for the driving conditions. Hopefully folks aren't buying these trucks for the type of acceleration experiments I was doing. Take my powertrain "review" with a grain of salt.

absolutely makes a world of a difference compared to the 5/6 speed alison 1000. i have quite the experience with LB7-LMM/ 7.3-6.4 and the 5.9 power train. i cut my teeth as a mechanic in that diesel era.

 

[21_6.7f450]

My silver truck runs at 2100rpm at 70mph. No, 1300-1500rpms unless I'm on a side road. If you are used to a car, I include 1/2 tons in this, you may see 10spds, DRWs, 500hp/1200ftlbs and 4.30 gears as excess. When hauling 35,000lbs or more it is not, I assure you. It is the little cars and 1/2 tons that zip around us, tailgate us, cut us off just to almost stop and turn right that have NO idea what it takes to control that weight-God bless duallies, have an exhaust brake and large service brakes-God bless them that can slow down when we are cut off and they turn right in front off us. 4.30 gears, a 10spd with low first few gears AND 500hp/1200ftlbs God bless em' to get the weight moving so this impatient car doesn't try to pass on the shoulder. The little Kia, BMW, Saturn, Nissan whatever cars don't need more than 110hp. More just makes the drivers more dangerous around us and the power goes to their head.
Nobody NEEDs more then a 2002 Honda civic. Are they compensating for something if they get a BMW, Porsche, Cadillac?
In the meantime I'll let em cut me off in my "BRODOZER" WITH big brakes that stopped the load from running em over.
If pulling just took horsepower, they'd use Formula 1 motors in semis. There is a little more than horsepower in the equation to pull a load. You also have to control it and stop it.
Horsepower is at the bottom of the list, handling and braking the weight is at the top. Sometimes excess is better.
Why would you "stomp" on someone else's truck, especially from a stop when you never mentioned a safety concern like getting rear ended? Overweight people have the most injuries taking off from a stop like rolling ankles, twisting knees etc...same with the truck. Mine never see more than 1/3 throttle until 30-40mph. Even after that not much more.

 

[wwillson]

I owned a 2018 Duramax with the Allison 6 speed and now own a 2021 Duramax with the 10 speed. I have towed about 40k miles with each. Zero modifications to either, completely factory.

I loved the 6 speed and I believe it's one of the most durable transmissions in a light duty truck. I changed the trans spin-on filter twice on the 6 speed and when cut, the filter looked like brand new. The first filter was slightly discolored and had a few metal flakes. The second filter, with a lot more miles, looked brand new. It had caught nothing. I would argue that it's important to dump the fluid early to get the bit of metal and friction material from break-in out of the trans.

I've never seen an auto trans that didn't slightly darken the ATF with clutch material. The fluid in the Allison looked brand new at both spill and fills. I have no doubt the 6 speed could make it to a million miles if cared for and was adult driven at factory power.

[cut open] Allison 29539579 spin-on filter for 1000 series transmission in Duramax

This is my first Allison filter cut at 8,000 miles: https://www.bobistheoilguy.com/forums/threads/cut-open-allison-29539579-spin-on-filter-for-1000-series-trans-in-duramax.297449/#post-4889368 I changed the spin on again today at 38,000 miles. Compare the first filter with 8,000 miles and 190...

bobistheoilguy.com

The 10 speed is also a great transmission. We pull a 20k pound trailer all over the country. The shifting unloaded can be a bit strange with what some people would call a "flare". The shifting under load is crisp, but never too crisp. As more torque is commanded the shifting becomes more and more crisp. When you are demanding maximum torque to merge onto an interstate, the shifts are extremely quick and crisp. You know in no uncertain terms that the trans shifted. The 10 speed also has the ability to lock the torque converter in each gear, while the 6 speed would not lock the converter in the first three gears. Without converter lockup, the 6 speed would put a lot of heat into the fluid. The 10 speed fluid has very little temperature rise even shifting under high commanded torque all the way up through the gears.

You can see from my 35k mile ATF and filter change that the 10 speed also puts very little material into the fluid.

2021 Chevy Duramax transmission pan replacement (PPE) and oil filter change

The truck (2021 Chevy 3500 Duramax) has 35,000 miles on the clock and I decided to change the trans filter and install a PPE trans pan. I do spill and fills on my transmissions. The 10 speed transmissions don't have drain plugs in their oil pans. This is highly annoying for those who do spill...

bobistheoilguy.com

Which trans do I prefer to pull with? It's not even a contest, the 10 speed wins in every category. I loved the 6 speed and much prefer the 10 speed.

 

[MrHorspwer]

10-speed starts in 2nd gear with the L5P unless you're in tow/haul mode.

The truck is literally holding itself back when there's no weight to pull. It's like a boxer pulling punches while sparring. Put them inside the ropes and ring the bell, there'll be a difference.

 

[21_6.7f450]

The 10L1000 and 10r140 are COMPLETELY different trans when you run them empty vs when you run them loaded.
Wilson said it best. That's how my 10r140 behavior is.

 

[wwillson]

10-speed starts in 2nd gear with the L5P unless you're in tow/haul mode.

The truck is literally holding itself back when there's no weight to pull. It's like a boxer pulling punches while sparring. Put them inside the ropes and ring the bell, there'll be a difference.

I will add that if you run the 10 speed in tow/haul mode when not loaded. It's not a smooth transmission. If I accidentally leave it in tow/haul after I unhook, it takes me just a couple seconds to realize my mistake.

 

[ls1mike]

I will add the 10 speed is a huge difference in the 6.6 gasser as well. Holds the engine speed right where it needs to be. Not even a contest to the old 6 speed. You need to get a load behind it.

 

[macarose]

This hardly counts as a new car review but it's worth something. Drove this truck home (35 miles), co-worker owns it. He had a CEL code I pulled up on my scanner. It was related to injector timing, deviation, something to that effect. I'm too lazy to look up the exact code. I helped him diagnose it and some research lead me to a GM TSB that basically read like this (cliff notes): this code will not cause any driveability issues, but certain GM trucks in XXX vin range need ECU flashed to newest software. It was a smoking gun, fit the issue to a T.

So I traded him a welding table (in back of truck) and got free fuel going home and back to work (that's worth at least $15 to update the ECU to latest software. He pays for the SPS subscription.

Back to the truck review. I'm not sure I could call it pure work truck trim. It has the modern conveniences like touch screen radio / driver instrumentation display (full tire pressure readout), 3 camera views, blind spot detection, LED taillights, heated / power "leather" seats. But the hard plastics everywhere felt cheap and said to me that this is far from a deluxe model. Made to work but offer relative comfort to the driver; I think it does an okay job at that.

Ride is smooth as glass over small imperfections. Hit a road surface transition, pothole, frost heave, etc. and it's quite jarring, putting it mildly.

The engine/trans combo is what has me stumped. I don't drive light/medium duty diesels everyday but I'm a blue collar worker and have driven plenty of them. This is easily the most latel model diesel I've driven, most of my experience comes from pre-2010 diesels from the big-3. I remember back when the Ford 6.0L Powerstroke w/ 5sp auto came out and that thing would put you back in your seat and hold you there as long as your foot was in it. Same with that era Cummins / Duramax. The 10 speed in this model seems to mess it all up. Stomp on it from a stop and naturally the traction control kicks in real quick due to tires wanting to spin, but once you're at 20-30+ and actually accelerating, you get a very noticeable pause at each gear change (which come quick and often) which sort of ruins the experience. So for the first few moments it feels semi quick, but then the climb to 60-80 feels nothing like what I'm used to with the older trucks. However butt dyno testing can be wildly innacurate .

I'm sure some of you are thinking "this isn't made to be quick" and you'd be right. I know it can pull, he routinely hauls 20,000#+ with it. I still had fun seeing what it could do and was left underwhelmed given the specs. Played with the exhaust brake and while it might be more handy pulling a trailer, it didn't seem all that useful with the truck unloaded other than making some extra noise. In normal driving it was extremely quiet and transmission shifted smoothly. I was never a fan of the exterior design on these, but I think I'm warming up to it.

View attachment 228594

View attachment 228595

View attachment 228596

View attachment 228597

View attachment 228598

Tell him it's his lucky day.

Purolator just started a rebate on their oil filters. Rockauto only offers one type of oil filter that qualifies for the rebate and it happens to fit this truck.

He can get three Purolator Ones which have excellent filtration for less than $1 after the rebate.delivered right to his home
Those filters collectively are good for 30,000 miles and 99% filtration at 30 microns.

He can also get two PUP 5 gallon bottle at Walmart in person for $48 since they're currently on rollback, and then apply their $25 rebate towards that cost.

These 6.6L engines take 10 quarts. If he's a DIY guy he can get his oil changed for less than $25. Plus he'll have two filters for his next oil changes which should come in handy whenever BITOG highlights another screaming oil deal.

Happy 4th!

 

[wwillson]

These 6.6L engines take 10 gallons.

The 6.6L L5P takes 10 quarts of engine oil.

 

[macarose]

The 6.6L L5P takes 10 quarts of engine oil.

Fixed. Long day. Thanks.

 

[21_6.7f450]

Car driver reviewing dually truck..lol
It rides rough and is big, oh and it drinks gas. This thing is bigger than my house.

Dually driver reviewing car..IE BMW 435 This thing is tiny!
This thing sits low enough to get stuck on my cattle guard. It doesn't have the power to pull my trailer...ooopppps I put diesel fuel in it. I drove this to my buddy's house and he asked why I'm driving my wife's car. CAUSE MAN it handles like a go-cart.