Re: What type of fluid you run in your axles?
Some people say 80w90 (which most manufacturers recommend) but yet I have read from other off-roading enthusiasts and experts that the heavier the better.
I, myself, buy the heaviest I can. I think the last time I got 90w140 Valvoline Semi-Synthetic. I can't remember, it's been a while. Anyway, it was the same price as the cheap no-name crap at $5.something/quart. Besides, I've changed it three times in the last 8,000 miles.
Once I decide what gears I'm going to run and change pinion seals I'll be switching to some full synthetic motorcycle gear lube. I'll probably do either Golden Spectro hypoid or some HRC crankcase stuff (any of the full synthetic stuff designed for wet clutches will probably do). I've had success in ATVs and Dirt Bikes with both of them. I figure if it can take my abuse in the quad it will be pampered in a differential.