your rear wheels are now fixed. Turn your prop shaft with one hand while you hang onto one of the drive axles. Then repeat on the other side drive axle. You should be able to see the freeplay if it is in either the diff or the drive axles. At 103K miles, you probably have both backlash in your ring and pinion, and freeplay in the two sets of drive axle joints. The drive axles are both easier and cheap to fix first. Our diffs are pretty stout and most guys do not have problems with them.