Many auto trans owners experience rapid torque converter locking and unlocking. This CAN be caused by a faulty APPS sensor. BUT often times is caused by the DIRTY CONNECTIONS or ALTERNATOR LEAKING AC current into the system. Below is a link I've included to test the alternator and to educate you on this issue.
Here is a link on how to install a torque converter lock up switch

If your having transmission issues with the torque converter locking and unlocking or 3rd-4th hunting,try these things first.

1 Clean battery terminals and body grounds
2 Clean ground strap at PCM located at passengers side firewall.
3 Remove and inspect the middle plug on PCM, this is the plug that contains transmission control wires.Clean with contact cleaner.
4 Remove, inspect and clean 8 wire plug located on drivers side of transmission
5 Remove, inspect and clean speed sensor plug located at tail housing of transmission, replace sensor if needed. It is an inexpensive sensor.

Here is a link to ATS Diesel showing a rewire that isolates the APPS circuit to the PCM in hopes to solve 3rd to 4th gear hunt and torque converter lock/unlock. I've heard from many folks that tried it and did not solve their issue. If you have cleaned all the connections and the problem still persists, I am actually with mopar1973man and believe this issue stems back to the alternator.