Rear Diff oil type.
I'm planning on changing the rear diff. lube on my 2000 Silverado, and my 2005 Suburban. Both have 4 wheel drive. According to the owners manual it recommends synthectic 75W-90 oil. I went to a local parts store and they did not have 75W-90. They had 75W-140, and 80W-90. I was told by the owner of the store that the Amsoil 80W-90 will work just fine. Just wanted to get some other opinions. The oil does meet the GM requirements. Thanks.
Jack the back of the truck up so the back wheels are off the ground. Put it in neutral spin a back wheel by hand, if the wheels go the same direction put the addative in. If one wheel goes foward and one goes backwards you do not need it.