Rear wheel bearing slop on a disk rear end will usually only become apparent once the caliper / pads have been removed and are no longer restricting the disk rotor / axle / bearing assy from moving in and out, the genuine GM Timken bearings last about 125,000 on a rough average, but with the caliper and pads holding the bearing together you won't feel the slop until they are removed allowing the bearing to move, generally there will be movement in an in / out direction felt and heard when turning corners more than driving in a straight line.
Once you can actually feel the bearing clunk they are realy stuffed, and that can mean the bearing outer may have turned inside the axle housing, big dramas then, as you then need a replacement diff housing, or a s/h complete unit from the wreckers, a good time to get yourself a LSD, the difference with both wheels driving is noticeably better on any slippery surface, no more easy woosy spinning of one wheel, leave two black lines instead if power permits.
Changing the rear bearings is not hard, remove the wheel and caliper and disk, the four bolts can then be undone through the largest hole in the axle plate, most will be tight if been there for a long time, remove the four nuts and put on the wheel loosely with the nuts on 1/4" and use it as a slide hammer, (a spare wheel without tyre good idea) and the axle should come out, just make sure the side your doing is 2" higher than the other or some oil will run out from the diff and contaminate the handbrake linings.
Its a good time to change the diff oil, brake pads and machine the rotors if needed and also fit new handbrake pads "usually" needed as well by the time a wheel bearing is shot, as even when new they seldom work great so adjust em up by the book if they have enough meat left on the linings.
Re-install the h/brake linings / axle assy, adjust the h/brake and your good to go, Note; one axle is substantially longer than the other so mark em L/R with some white out on the outer axle plate, remember they need to be sent to someone with a press, although a length of steel pipe will do the job if carefull, the collet has to be on square and pushed all the way home.