I wonder, when you say gradually - was it intermittently worse? Mine quit shifting after a fluid change and then sometimes would work fine for a long time, then stop shifting for a while. Did all of Cruiser's steps and found a bad NSS, and replaced TPS with voltages in range. Still intermittent for a while (seemed like it needed to warm up, or maybe it was after driving through a deep puddle, or maybe after a dry spell with no rain, etc. etc.). Now I just shift manually, so a new to me TCU is my next step, I guess.

 

A stop lamp switch malfunction can effect the operation of the brake-transmission shift interlock feature so the transmission shifter would not be able to shift correctly. It deals mostly with the Torque Converter disengagement though. It is just one of the other electrical components located on the transmission circuitry. It links to the Transmission Control Module (TCM), the Powertrain Control Module (PCM), and the transmission solenoids. A faulty brake switch can cause some vehicles to go into a limp mode. If the brake switch has an intermittent fault it may cause the transmission to go into and out of gear too. Ultimately, since it is linked up to the PCM, TCM, and the transmission solenoids; depending on the actual primary fault influence of all of the involved electrical.. it is possible to have an influence on transmission shifting characteristics.

If all of the other avenues you pursue are failing to resolve the shifting issue your Jeep is having right now, it may be worth it to look into the brake switch to see if this might be the reason.

And Larry.. Maybe starting your own thread specific to your Jeeps exact issue as how it is occuring on your Jeep may also help you in getting better response too.

 

Thanks! great suggestions. I'll look into it today and properly post if still no luck.