2000 Chevy 2500 HD 6.0l Vin- u, Clunks when shifting from park/drive/reverse

I have 2000 chev 2500 hd, its a great truck, it has 140, some odd thousand, but lately I have noticed a clunk when shifting from park to reverse, or park to drive or reverse to drive or drive to reverse, i have not a clue on were to start on fixing this problem. any advise would be great! thanks

The noise might be from a worn U-joint.

To confirm this, raise the rear tires off the ground. Place the transmission into neutral. Grab one of the rear tires and rotate it back and forth while observing the U-joints. If there’s a worn U-joint it’ll be obvious.