I have a fleet side 57 f100 with original 272 and 3 speed tranny. I recently converted it to 4bbl and threw on an efi kit from fitech. Everything went perfect until I tested it on some large hills in my neighborhood. The truck just sputtered and died. The efi tried to keep it alive but couldn't. I thought at first it was timing but I confirmed the timing was good.

Do I need to do something to the transmission? It is all original so almost 60 years old. I don't know enough about transmissions to say for sure. Is my tranny not able to support the new horsepower?

It does not have the auto option on the tranny either.

Thank you all in advance for any help you can provide.