Quote Originally Posted by MacDR50 View Post
What rear and front axles do I have or how can I tell? My rear is locking and I have a 4X4. I intend to tow at least 11,000 lbs. I didn't read anything about changing my lubes after a break-in period. The truck hasn't towed anything yet. I intend this to be my last truck so it has to last at least 10-15 yrs and if I look after it and myself maybe longer. I can do all my own fluid changes as I have access to a lift.
All Duramax equipped trucks are the same. The rear is an AAM 11.5" axle. If it has a locker, it's the Eaton Gov-Loc. The front is a GM Corporate 9.25" IFS (I could be wrong on the size). The only gear ratio offered for these trucks is 3.73.

Changing the rear lube at the right time can be important. Once you've seen what comes out, you won't ask why (reminiscent to those with newborn children). And, soon after you begin towing a significant load (11K qualifies). Originally, we recommended a change at 5K with no significant towing. Or, after 500 miles of towing. If you are keeping your rig for all eternity (relatively), it could be different. Lube changes are cheap, and easy. Money very well spent early on. Work hardening and cleaning of the assembly junk is important for long life. In your case, I recommend an initial change (if over 5K), then another change after 500-1,000 miles after a significant towing experience. Also, be careful to not overheat the diff, which is easy when towing and new. Frequent stops (every hour or so) with a cooling period of 15 minutes is good. This ensures thorough work hardening of the gear set. You should have to do this for more than the first 500 miles or so, of towing. DO NOT use dino lube in the rear end, under any circumstance. As we've seen, the brand of synthetic lube hasn't shown any noticeable difference. As long as it's full synthetic (none of that "mix" stuff), it should be fine with any of the popular brands.