Okay. So, I've been trying to figure this out for a few days.

I'm having these problems:
1) Loud clunk when I'm switching between park/drive/reverse (any combination)
2) Occasionally, a knocking noise that sounds like it's coming from the rear of the vehicle while it's in drive or reverse.

I took it into a local shop and asked them to check the u-joints on the driveshaft because my Chilton manual matched these symptoms up to worn u-joints, but they told me the u-joints are fine and its the ring & pinion thats giving me my problem.

Wanted to get everyone's opinion on what they said versus my manual...

 

Crawl under your truck and check it out yourself. Chock the front wheels, jack up at least one rear wheel, put the trani in neutral & release the parking brake. Turn the drive shaft by hand to see where the play is. If the u-joints seem tight and there appears to be a lot of rotational play in the axle flange, then the ring and pinion gears are worn.
...Terry