It�s bang shifting because it has detected slippage and entered limp home mode. Shutting off the engine and restarting clears it until slippage is detected again.
You really nee to do some trouble shooting like using a scanner to compare the TSS to the engine RPM during lock up, or just look at the control pressure during the bang shift (I bet its 90 PSI or higher), or, test for codes when it bang shifts.
Again, it is rare for a TC to just go bad, It usually a stuck vale that takes it out.
jeff
