Could be worn bearings, improper backlash on the gears, etc

Just to make sure, you don't have an aftermarket locker in the rear end, like an ARB, do you? That will give you quite a bit of slop.

88 4R, 350 V8, R150 5 speed Sold <...uot; />
97 4R, stock, daily driver
98 Sienna, kid and dog hauler, wife's ride