2004 Colorado - Need diff./xfer case suggestions

[mshu7]

Truck:
2004 Chevy Colorado / 3.5L I5 / Auto Trans. / 4x4 / 85,000 miles

Other than engine oil, all fluids are factory fill. I do all my own oil changes and other routine maintenance. I mostly drive this truck around town, with the occasional highway venture. Between May-October, I tow a small 16-ft. aluminum Bass Tracker fishing boat a few times a month to lake about 50 minutes away (some highway, some rural roads). At 90K, I plan on doing an ATF flush/replace filter as well as a drain/re-fill on the diff's and transfer case (among many other things).

Manual calls for:
Transmission - Dex III
Differentials - 75w90
Transfer case (Isuzu T150) - Synchromesh 5w30

Since I want to do a complete flush on the ATF, I'm going to take it to a reputable shop that I use for things that I can't do myself. They carry Valvoline products so I'm going request Maxlife ATF. My dilemma is what to do with the diff's and transfer case. Here's what I'm looking at:

Option 1:
Drain and re-fill diff's and transfer case myself (it will be my first time doing either of these on any vehicle) and spend a little more money on fluids (ie - Redline or Amsoil).

Option 2:
Just let the shop doing the ATF flush handle the diff's and transfer case. I'd request Valvoline's Synthetic 75w90 for the diff's, but I'm not sure what they'd use for the transfer case.

If I do the diff's and transfer case myself, I'd go with Redline 75w90 for the diff's, however, I don't see anything on Redline's website regarding synchromesh fluid. Do they not make anything for it? If not, would Amsoil Synchromesh 5w30 be my next best option?

Lastly, what would you guys recommend for drain intervals on all these components? After the ATF flush, should I start doing a drain/refill/filter instead of flushes? The service manual that came with the truck leaves a lot to be desired.

I would greatly appreciate your guys' opinions/recommendations on everything? Thank you in advance.

 

[unDummy]

ATF: any DexronVI or full-synthetic DexronIII equivalent. Maxlife is a good choice.

Differential: any full synthetic GL5 75w90 gear oil. Since you do a little towing, I'd use a 75w110 synthetic in the rearend(or 50:50 mix of 75w90 and 75w140).

For the x-case: BG SynchroshiftII, Redline MTL, or Amsoil MTF...should be used. Pennzoil Synchromesh is also available at various auto-parts stores. Nothing wrong with that and price is right.

Since 80k+ plus is a lot on OE fluids, I'd u$e whatever was available at the shop or local stores. Run them for 30k, make sure vehicle doesn't have any unforeseen maintenance/repairs, and then order Amsoil, Redline, Amalie, BG, Royalpurple, whatever for the next round of maintenance @120k.
You have a lot of maintenance that should be considered concerning belts/hoses/thermostat/brakefluid/brakes/tires/PSF/filters.

That being said, store brand, Valvoline, Castrol, Mobil 1, Pennzoil.... have gear oils that you can use for now from your local store at a reasonable price.

 

[mshu7]

Lots of great info! I will put it all to good use. Thank you very much UD!

Edit: This was my father's truck but he past away a year ago so that's why I'm just now getting to all this maintenance. I've done a few things already though since getting the truck at 70K:

Air filter - Replaced at 80K.
Serp. belt - Replaced around 75K w/Goodyear Gatorback.
PS Fluid - Turkey baster method replaced 2-3 times with Lucas PS fluid (all they had at the store I went to).
Front Brakes - Slapped on ceramic pads around 80K (rear drums need attention).
Tires - My dad had put Goodyear Wranglers on at 50K (not my favorites at all).

I've still got quite a few things to knock out when it turns 90K, as you mentioned.

 

[wapacz]

don't forget your break fluid.

also dex6 has been back speced for gm transmissions. It has to be atleast partially synthetic to make the spec.

 

[mshu7]

Thanks wapacz! I'll bleed the brake fluid as well. I decided on Maxlife ATF based on the positive things I've read on here, plus it's synthetic.