Transmission problem surging at stop

Whenever my truck is at a stop or in reverse the truck will surge and die. Throwing it into neutral can save it from staling. The truck runs perfectly otherwise. Mods are a river city diesel low stall converter, elite clutches pack rebuild kit and a elite input shaft. Transmission has been out of the truck twice.truck threw a clutch pack and solenoid d code once but cleared it and hasn't thrown one since. Truck is a 4x4 if that matters. Also we changed our the upper belt tensioner and that's when the problems began. Thanks in advance for any input

What is probably happening is that the torque converter clutch is drifting on. That can happen when line pressure gets too low. A bad solenoid, low trans fluid, internal leaks, worn pump, or a bad converter are all possibilities.

Truck has a teams go shift kit if that matters, so should I try adding fluid or just take it to a shop?

Is the fluid low? If it is add fluid. If it's now low on fluid, then take it to a shop because it's going to need to be pulled and checked out.

Update, took the truck to a transmision shop a few weeks ago where they put a new so solinoid pack in and turNed the truck using DPF on tunes power set to stock. The issue has completely gone away. Thanks for the input on the problem guys!