Well, there is a rear diff no matter what, if you have 4wd you also have a front diff and transfer case to think about. Do yourself a favor and go buy one of the suction style fluid pumps, it makes filling the diffs much easier. The rear diff fill plug is easier to access if you drop the spare and leave the ebrake off. The transfer case is right in the middle behind the tranny and very easy. The front diff can be trickier, it is best to remove the whole skid palte assembly, it is 2 pieces total. Then you need to have allen style sockets, I would have to look at mine but IIRC the size is a 12mm, might be a 10 so check it before you buy. Its always a good idea to free the fill plug first, that way you don't have an empty diff and stuck fill plug, a little PB blaster will help them come off easier. It is very easy to round off the front plugs so be careful. Be sure when reinstalling the drain plugs to put the magnetic ones in, the drain is magnetic on both diffs and fill is not, transfer case both are not. Some replace the crush washers every time, I do not and have never leaked at all, use your judgement here, if they look bad get new ones. 75/90 all around will work just fine, manual calls for 2 viscosities I believe. Also get a grease gun and lube the driveshaft while under there, 2 zerks at each ujoint front to back. Then how about spark plugs, pcv valve and coolant flush.
