I have an 01 Silverado LS 1500 4X4 with the 5.3L and 4l80e combination. Every time I shift it into reverse it makes a clunking noise. I replaced the u joints on the front drive shaft because there was some play. No difference. Rear drive shaft is fine. I do have quite a bit of play in the rear end but I watched under the truck as a friend shifted it back and forth there was no movement. Any ideas? Thanks in advance!