Show it to me in the GM service manual or owner's manual ('99 and up Silverado) :w2:

the only reason to change diff oil is if something else goes wrong and you have to perform maintenance on the actual diff or carrier...other wise leave it alone and worry about something else...that oil will be fine in there

haven't looked in the owners manual, but it is in the fsm

I went 35k before I changed mine.... and I was amazed at how much metal was stuck to the plug(s)....moreso the front than the rear. Definitely recommend changing both probably around the 3k mark for the first time and then probably 50k after that if you use quality oil.

First oil change at 65k. Not by choice, but needed to change seals in the rear hubs. It was relatively clean. Changed at 110k, this time more metal, but lot harder towing after the hub repair. Pulling 10k at 85 - 90 down the interstate for 1 hr in and out of traffic does not help. Also added the power adder at 70k. Oil still looked and felt ok, not an excessive amount of metal on the magnet, but some there. Using amsoil in the rear diff now. Need to do the front, but don't have the time or oil. Also changed the trans case to amsoil from the stuff that GM recommends, after the t-case hole issue.

Go with Amsoil gear oil. GM rear end oil failed a stress test of some sort. The guy I get my Amsoil from showed me the test failure. The oil is a little bit more expensive but worth it.

Oil Change
 

If you do a gear swap or you buy a brand new truck... Change the rear end oil after 500 miles. During that first 500 miles the gears are wearing themselves in/breaking themselves in. And there is going to be some metal shaving from the gears wearing, doesn't matter if its a gear swap or just a brand new gear set, the oil needs to be changed. After that we have always done it with at the same time we do tranny fluid, 60,000 miles. Every 60,000 miles and just check it every motor oil change. We do this on all our trucks. Last three we had were still running strong at 360,000 miles but the seats were so damn wore out we sold em.
Something to think about if after you do you first oil change and you have some metal shavings larger specs or fine powder its not a bad idea to do another change about 1,000 miles later. Hope this helps...:U:
oh yeah we run mobile 1. IN EVERYTHING!

first service on the diff was with gm oil. Several thousand miles ago, changed the rear hub seals (again) this time went with Amsoil. Swapped the tranny a while back to amsoil and the motor has been on Amsoil for almost 100k now.

I even swapped the transfer case to the same oil I use in the diffs. The GM owners man is vague on the lube used. They specify a special oil for the auto diff case, and it sounds like they are talking about the electronic shift when they mean the diff case that is built for people who do not know when to put it in 4wd.