Torque converter lockup just connects the input and output of the torque converter. It's normal and happens from 25mph on these cars.

Not sure what else could cause the lockup, maybe parking pawl?

 

So to be clear, your rear wheels locked solid at speed? Both, or just one?

There aren't many things that are capable of doing that- the parking pawl
will shear, the driveshaft will break, etc. etc.

This is one of those things that we can speculate about on the internet
for days, but without your car in front of us, the little clues that point
at the culprit are probably going to get missed.
For a gross fault like this, you're going to want a mechanic who learned
how to work on these cars when they were new.

imho.

t

 

I believe my torque converter has been locking up.

The only bad thing happens with a locked up TC is when car stopped at the traffic light -- stall the engine. It's nothing wrong with a locked up TC with a car moving. Your problem is in the tranny: something that locked up the output flange. Tranny has to be opened up for inspection.