I would find a reputable trans shop and have them diagnose it. Or at least get it scanned by someone who is familiar with the scanner and transmissions.

Sounds like you'll need tranny/drivetrain work anyways. So unless you're going to DIY ...

I definitely would not just buy a torque converter.

I had mine diagnosed and let them keep it overnight. They could not replicate the problem. They refused to charge me for anything.

I slipped the guy $20 anyway when I went to pick it up.

Also, if it was me I would go the rebuild route. It's a little less than the remanufactured and you don't have to worry about any coding.