Went to back out of the driveway this morning, and when I put it in reverse there was a clunk, and the psd stalled. Started right up and did it again when I put it in reverse. Any ideas before I take it to the shop. Thanks

 

Low trans fluid, loose/fell out internal filter, worn seals, worn pump, bad torque converter, stuck valve, short in the wiring to the torque converter solenoid, or a bad torque converter solenoid. Those are the reasons it could be happening off the top of my head.

 

Finally got the truck back after 6 weeks at the shop. Torque converter destroyed itself. Shop did a hd rebuild then couldn't find 2 parts to finish it,and had to wait almost a month to get the parts and finish the job.