My 1990 Ford F150 Transmission Problem

I bought a 1991 Ford f150 with a rebuilt engine of a 1990 Ford f150 with 4.9L V8. However, recently, something happen with my transmission and it would not go forward at all. Furthermore, when I shift gear my Ford will just suddenly turn off without me pressing the gas. I need help you guys, please tell me if I need a new transmission or there's a cheap way to fix this problem. Thank you very much you guys.

F.Y.I. My transmission is an automatic.

First is the transmission full of fluid. Did you try to get it to move in reverse before it stalls. Thus all sounds like the torque converter is bad. Find local shop at ATRA.COM for more help. This won't be a easy back yard repair

F.Y.I. The 4.9 engine is a straight six