Just checked the manual for the '99 4.8 gasser I just picked up, For the autotransfer case is says to use Automatic transfer case fluid # 12378396. The dmax just used Dex 3, What is the difference? can I use dex 3 in the 1/2 ton transfer case? Also, the rear is a G80 locking rear, although obviously much different than the Dmax G80. Mobil 1 75-90 worked great in the Dmax, will it work in the 1/2 ton? I ask cause I used this lube in my '97 formula and had to add the limited slip lube from GM cause the rear made a terrible racket after I changed the fluid! And how about the front, book says 80-90, I assume the same 75-90 will work in the front diff? Thanks for any help, figured I'd try here before going to the silverado site or something!

Actually the locking mechanisms for both axles are the same, just different sizes. Most gear lubes have the neccessary stuff for these axles. Chattering is usually a sign of dry clutch plates, do some figure 8's in a parking lot to slip plates a bit. 75-90 should be OK for front, check lube classification to be sure (API GL-4 for example). Not sure about auto trac... check with dealer to change over part #... may be special lube