I think the rears are the same from early '99 thru '04... the diffrence in the early '99 and later trucks seems to be limited to the front end and front suspension... rotors/unit berrings/ubolts and plates/track bar/etc.
The rear wheel berrings take a special hub nut tool, you will need that, should be availble from a parts store with a lone-a-tool program such as autozone or advance a.p.
If they are lose and you've been running them that way, I would replace them no questions asked. I just did rear wheel berrings on my work van... started out as a brake job... turned into rotors, calipers, pads, emg shoes, wheel berrings, and exhaust work... almost ended up striaght piped! Had an old 3.5" straight thru muffler that was put on due to the "work truck with my name on it" factor. And my rear berrings wern't lose, they just had wear marks on the races. No reason to put it back together that way.