Any 2014+ Sierra/Silverado owners out there?

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Greetings BITOG - with two kiddos and another soon on the way I'm looking to upgrade to a used 2014+ GMC/Chev. full size crew cab sometime this spring/summer. It's a hassle to get car seats in the back of my '98 K1500 which leads me to rarely drive it. Will likely sell the '98 to my dad for a weekend 4-wheeler hauler.

Anyway, I've decided most likely on a GMC (like the grille better) with the crew cab and short box (need it to fit in the garage). But I'm not sure about engine or transmission configurations. I've driven several pre-2014 5.3s (good engine, but lacked in torque) and own a 2007 6.2L in our Yukon (great engine). I'm not sure how the newer "EcoTec" engines stack up in the newer models, and if there's any reason to pick one over the other, reliability wise. My observation is that the 6.2L gets nearly the same fuel economy as the 5.3L in the 2014+ trucks, so that's not an issue for me (unless real world use varies greatly from EPA estimates). I think I would like the extra power of the 6.2L, but if the right 5.3L came along (price, miles, condition) I would spring for it. I've also heard some people complain about the 8-speed transmission, and prefer the 6-speed. Seems like the '17-'18 models with the 6.2L usually are mated to the 8-speed.

So, I need some opinions from any 2014+ GM full-size owners:

  • Any reason to spring for the 5.3L or 6.2L? Would real world use equate to major fuel mileage differences between the two engines?
  • Is the 8-speed or 6-speed transmission more desirable?
  • Are there any "gotchas" with these models that I need to look out for?


Thanks in advance for any opinions / insight offered!
 
Some of their trans are prone to have a very noticeable CLUNK at very low speeds. A friend that has a 2014 has this problem, and even my sons 2016 GMC full size SUV has it. It's been in the shop three times for this.
 
We have a 2018 V6 2WD (6 speed) and the mileage is outstanding - 22 mpg highway @ 70mph. It's a work truck that usually carriers about 800lbs of gear (w cap) and we don't tow. I'd probably spring for the 5.3 if you are going to tow a light-med trailer, or want 4WD. Personally, I think the 6.2 is overkill for most people, and the 8 speed is going to be a lot more expensive to repair. GM transmissions have historically lasted 90-120K before a $3-4K rebuild. Try to match your axle ratio to maximize your mileage. Engines with less torque tend to be easier on the transmission.
 
Have a 2017 Tahoe and 2018 Z71 … no clunk, but punked a punk who thought he was fast enough to cut me off (again) with his 2010 Silverado … one of the endless lane changer and shoot the gap types … and my 2018 left him hard on the brakes …don't normally engage in this type of behavior … but checked 360 degrees and gave him some feedback …

Even the G80's don't clunk … AAM still my favorite rear gear set on/off the road …
Really like the ecotec and 6L80 combos …
 
I've had two of these trucks: First was a 14 Silverado w/5.3 and 6 speed. Great truck no issues in ownership although I didn't have it long as it was a lease. Gas mileage was great and it was one of my favorite all time vehicles. I now have a 17 Denali. It also has the 5.3 but has the 8 speed. The 8 speed is quirky. Biggest gripe is the 8 speed until warmed up. I have a stop sign about 1 1/2 miles from my house. I have to pull out into a busy US highway @ this sign. Sometimes when coming to a stop the tranny doesn't shift down into lowest gear. When you give it the go juice it tries to take off in 2nd or 3rd gear and slams into 1st. Only does it once out of maybe 20 times, but it does create a "oh $***" moment. Also sitting completely stopped the transmission will downshift (you don't know it hasn't already) from 2nd to 1st and the truck lurches forward If your foot isn't on the brake firmly you could easily hit a vehicle in front of you. This has happened maybe 2-3 times in the last 6 months. 99% of the time its very smooth and I have no problems. Gas mileage is great and the 8-speed does give the 5.3 way more umph than with the 6.
 
I have a 2017 Sierra with the 5.3L and the 8 speed. Like some of the comments above, the transmission can be a little goofy until it hits 120 degrees. After that, everything is great.

The only other complaint I have is with Android auto. I had a Pixel XL and Android auto used to randomly reboot while using it. I switched to Apple Carplay and everything has been great.
 
I have almost 150,000 miles on my 14 Sierra. Overall it's been a good vehicle and has never left me stranded. It's far from perfect but hasn't required any major repairs. I do most maintenance myself. Here's my 2 cents.
- If you find a truck you are interested be sure to test drive it at highway speed. These trucks are know to have vibration issues (Google Chevy shake). Mine has a slight vibration at 75 MPH and noticeable at 80 MPH. I've heard of some having it lower speeds. Finding the source of the vibration seems to be an issue. Some have had success with balancing or replacing the driveshaft. I've read that some had their axle replaced and that did even solve the problem. I don't think GM has found the smoking gun (or won't admit what it is if they have). I tolerate mine as I rarely drive above 75 MPH.
- Most complaints (including myself) regarding the 6 speed are due to the factory computer programming. It's set very conservative and wants to get into 6th gear ASAP. This can cause some lugging when trying to accelerate. This programming combined with, in my opinion, excessive "torque management" can create a numb and sometimes frustrating driving experience. I did an aftermarket tune on my Sierra that helped alleviate some of this (raised shift points, reduced torque management, increased throttle response).
- It does seem that the 6.2 doesn't get much worse mileage then the 5.3 (maybe 1 MPG on average). I have the 5.3 and it's been sufficient for my needs (3,000 lb boat). I imagine it's more difficult to find a used 6.2 vs the 5.3. Just don't seem as common.
- Anytime the 5.3 is brought up, a lot of people talk about oil consumption. This does seem to be a problem with the Vortec AFM (V4 mode) engines. I burn maybe a quart over a 7500 mile OCI and I haven't heard much complaining regarding excessive oil consumption with the new Ecotec 5.3. GM appears to have fixed this problem.

Here are some main items I have had fixed/upgraded (most while under warranty).
- Multiple computer updates (recalls)
- Loose driver seat (semi common problem). Dealership installed kit which fixed problem.
- Wind noise coming from driver side door. Dealership adjusted door and noise was reduced substantially
- One of the rear shocks began to squeak. Could have had it warrantied but decided to replace with Bilstein 4600 series. Squeak went away and ride improved slightly.
- Most of my frame is covered in rust. The waxy coating GM uses doesn't stick very well. Majority of it had come off within the first year (exposing bare steel).
- Swapped OEM bulbs to HID's. Factory bulbs are inadequate. I believe they even issued a computer update that increased voltage to the bulbs. This is on the GMC's with projector lamps.
- Swapped OEM front shocks to Bilstein 5100's set to 2nd highest level. Gave me about 1.25" of lift and a noticeable improvement in ride quality. Would highly recommend. If you don't want to lift then get their 4600 series.
 
Thanks for the responses! I think I'm leaning toward a 5.3 unless I find one with a 6.2 that meets the rest of my criteria. Our Yukon has the 6-speed, and I would note that it also shifts into 6th gear earlier than I would like, causing it to violently shift down a few gears when giving it some gas at 40-50MPH speeds. The other thing I notice is when slowing down/coasting to a stoplight and then accelerating if the light turns green. I often get a big "CLUNK" as I hit the gas, and the transmission downshifts at the same time all of the slack in the drivetrain tightens up. I usually avoid this by applying really light throttle until all the drivetrain slack is out, and thus no clunk when I get back into the throttle.

All this to say, at least in my 2007 6-speed, it sometimes exhibits quirky behavior but I've gotten used to it now. It sounds like most of the issues with the 8-speed are TCC shuddering issues that seem to be resolved with either a full transmission fluid flush with the new Dexron HP fluid, or a torque converter replacement.
 
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