I was having TB issues with a 96 legacy that I picked up from my brother (it had died - fuel pump/cat/O2 sensor issues)
Flushed tranny fluid 3X and added lubeguard (got at O'Reilly's) in the red bottle.
Helped a little, but still had TB. Also tranny shifted hard from 1-2, and shifted erratically at times ever since I got it running.
Took off the battery end of the ground and cleaned it and added auxiliary grounds to the chassis and engine - didn't solve problem.
A couple of weeks ago I took off the ground cable on the started end and wire brushed the contact surfaces and tightned. Ohmed the cable out at the same time and was good. I also removed the dash and removed all the connectors to replace the dash lights while I had the tools out.
Now no more hard shift and no more TB. They both went away at the same time, so I don't think it was the tranny flushing. So I don't know if it was a ground issue, and I don't know if the dash panel has a speed sensor circuit in it that could affect shifting. The problem has not re-surfaced for a couple of weeks now, I hope I have it fixed.