92 Noise in drivetrain

92 2wd v8 auto
has clunk noise when placed in reverse. The u-joints are fine. It sounds to me like it is in the rear of the transmission. The owner states that he has put a rearend in the truck one year ago because of it locking up. He thinks the rearend that is in it now is doing the same thing.
Any help on the noise and how to fix it would be appreciated.

Check the transmission mount. Also check the freeplay in the driveshaft with the transmission in neutral and the parking brake on. There should be about 10-20 degrees of rotation. It's not a proper backlash test, but gives you a good idea if you need to pull the cover.