I'm cheap, so I always use Valvoline Synthetic gear oil in 75-90. Never had a problem with gears, lockers, limited slip, etc. It was recommended by a few people who make a living off of drivelines.
Transmission and transfer case I always have run Mobile One full synthetic. Runs much cooler with synthetic. Since you don't have to change out the transmission / transfer case fluid very often, its worth the money.
Engine oil, I just get whatever is cheaper brand name 5w-30. Change it every 3000 miles, or yearly, whichever is first (usually ends up being yearly). That reminds me, I have changed out all the fluids recently, except for the engine oil.
If you are able, drop a small, powerful magnet in the recess in the bottom of the 8.8 housing, or the diff cover. Cheap monitoring device.