Automatic stalls in reverse.

Hi - I have a 71 Duster column shift automatic with a 360 engine with less than 400 miles on it. Rebuilt transmission as well.

Has been running great but all of a sudden it completely shuts down in reverse. Started doing it randomly 2 weeks ago but now it is almost constant.

Shift linkage seems to be fine. Opened steering column and did wiggle test on the wires but could not get any clues from there.

Any help would be appreciated.