Torqueflite won’t shift to second engine is dragged down

Hi all, been a while.

My Stock 66 Fury III 318 Poly is having a transmission problem today. The transmission was rebuilt about 5k miles ago. When I put it in reverse to back out I heard a loud sudden ping or bang sound. The car backed out fine and went into first fine but when it shifted (or tried to shift) to 2nd it was like I had put my foot on the brake and the engine would almost stall. It would then continue to stay in first and would keep trying to shift to 2nd with the same result.

Reverse works fine. Fluid is full and red but might smell a little odd? Now about 2 years ago I installed a 4 barrel carb and had adjusted the kick down rod so it would downshift sooner (or so I thought). After reading a bit about it I was wondering if the kickdown being mal-adjusted would cause this sort of failure? Where would the failure be?

It seems to point to the govenor but the binding and the bang make me think a band or something more serious?