Originally Posted By: Bill in Utah
If you have a LEVER on the floor, then you use a ATF fluid in the transfer case.
ANYTHING PUSH BUTTON you need the fluid avail ONLY from GM dealerships or online.
On your rear diff, you may need 85-140 gear oil. Check in your manual as it will state what you need.
My truck has the lever and I use Supertech AFT fluid in it. The front diff has Supertech 75w-90 and rear end has Amsoil 75-90 in it. Works like a charm.
Take care, Bill
INCORRECT!
You have a 2500HD so you do not have an "Automatic" T-case. You have an Electric shift model. Same as the floor shift except done by pushing a button. "Automatic" means the t-case shifts in and out of 4wd as needed.
Yor diffs take 80w-90, UNLESS the rear diff is the Eaton locker. Look for RPO code G80 on the sticker inside the glove box. The G80 uses a synthetic 75w-90 only available through GM (expensive). However, many have used other products without any problems.Also, the manual says a 75w-140 may be used in a truck that sees alot of towing.
FWIW, I have Mobil1 ATF in my t-case and Mobil1 75w-90 LS in both diffs. my Locker works fine.