Were you able to communicate with the ETC just prior to changing the transmission?

Why was the transmission changed?

If loss of communication occurred immediately after changing the transmission, disconnect the transmission plug ( Right front of transmission. ) and try to read the ETC.

If the ETC is visible, the transmission is pulling the system down. On other systems I've seen sensors fail and pull the 5 VDC supply down.

If the ETC isn't visible, look for a pinched wire near the transmission wire.

For a 1997 car that uses the 38 pin underhood connector, the ETC does not need to be plugged into the rest of the car or the transmission. ( I made an out of car test harness to look at all modules on the 1997 cars )

At some point, all testing moved to the under dash OBD2 port. I have not tested this system but everything should talk through the CAN bus system.