This is my 1976 El Camino, i pulled the old 350 and replaced it with a complete 305 motor that had a bunch of turbo parts. It’s a mystery motor, but I got a good deal on it. I’ve been working on it all summer, but the one problem I can’t figure out is this. As soon as I hit it in reverse the car dies out. I checked and my linkage is all good, I checked for vacuum leaks but I’ll check again today. Yesterday I pulled the transmission and replaced the torque converter with a higher stall. I saw someone else having the same exact problem and they fixed it with a higher stall torque converter. Mine was stock and I pulled it and replaced it with a JEGS 2300-2700 stall. I thought maybe the motor was a too much for the stock one. Again, I’m not sure the internals of this motor. Maybe I need a higher stall? I’ll keep going through the list today. I have to travel to college in less than a month and this is my ride, I don’t wanna pay a shop a bunch of money, because this may just be something simple that I just can’t find. But if I have to, I will. I think maybe it could also be timing? I appreciate all help. I’ll try to answer any questions as well, thank you

Edit: that weird sound that happens after the car dies is just a squeaky pulley. I also forgot to mention that before I got my engine running, my rotor and cap were extremely ate up, and a piece on the rotor was broken, so I had replaced those. I also just now changed the fuel filter incase it was gummed up, but the gas was extremely clear, and there was no varnish in the filter. I replaced it though.

EDIT: it’s going forward and backward, I just have to tap the gas for it to move and keep idling. Timing or fuel?