PCU = Jeep's brain...the computer that runs all the electronic stuff. Also known as PCM...As for the unexpected stalling...We have replaced all modules, and sensors; just recently found out that this particular model jeep (Grand Cherokee) has a faulty wiring harness and that is very difficult to replace. If you can fine one - it's gonna run around 850.00$ Newer models (1998+) may still have parts out there for replacement. Even the Jeep dealerships have trouble finding or making harnesses for the older models.
Hope this info helps.