I put Amsoil synthetic 80w-90 in my diffs and transfer at around 60k. I just changed the front and transfer at 160k and the fluid looked great (slightly darkened but not black). Just a little metal powder on the magnets. I still need to do the rear. I put in Amsoil Severe Gear 75w-90 and don't expect to need to change it for another 100k.
Regular drain and fills for the transmission (Look for 100% change in 30k for standard fluids, extend that for full synthetics. That's around a drain and fill every 10k).
Power steering fluid gets a workout in these trucks. I do about the same as for the transmission. I have an inline filter installed and will soon pull it out and open it up to see if it has caught anything.
Brake fluid needs replaced every three years or so.
For driveshaft info check - The OFFICIAL clunk/thunk driveshaft thread
