Trans Snafu and ???

There could still be an internal issue with the torque conveter that you can't see from the outside. Found out this the hard way yrs. ago. A bud of mine had his 75 Fury stop going in all gears and he went to the junkyard and bought a different trans. that was known to be good and it didn't come with the converter so he reused his old one. Put it together and still nothing. Pulled it back out and put in a new converter and worked great. Not sure what broke in the converter but something did.