2001 Ram 2500 re 46 5.9 v8 gasser. 75k miles. 2wd lb. reg cab. It is driven once a week. The transmission clunks when I give the engine gas initially from a stop. . Shifts fine and positive. Downshifts well. I did have it rebuilt, with a new converter and an upgrade on the solenoids. Trans cooler.
If I am cruising along with my foot off the gas and accelerate it thunks. It is not slop in the ujoints or differential. If it was a manual I would guess end play.
Longest trip it has seen was 200 miles. Use it for towing cars on a trailer on occasion and dump runs.
Is it something to worry about, because this revitalization has got me at the end of my patience.

 

Can you post an audio file of the noise??

If the trans is staying in gear, then it likely is slop somewhere in the system. Or possibly a bad mount somewhere....

 

Have you checked the pinion nut at the differential? And also is the driveshaft a two piece with a rubber boot on it? If you have the rubber boot on the driveshaft. Peel it back and fill it with grease.