a bad torque converter will start showing itself early on when shifting between 2nd and 3rd gear. You will feel the car shake when it shifts. If not addressed properly, the shudder will start happening between other gears and eventually kill the transmission. I have not heard of a transmission causing a car to do what you are saying. vacuum leak, yes, timing issue, yes, but never a torque converter. When I have experience this in the past, it would spit and sputter and eventually backfire if timing was the issue.
Does it still have cats on it? potentially are those plugged?