The symptoms you’re describing, especially with the multiple U codes and limp mode activation, could indeed point towards a communication issue within the vehicle’s electronic systems. Since you've replaced several key components, it’s good that you’re considering wiring and ground connections next, as these can often cause erratic behavior in the Jeep's electronics.
A few things to check:
Wiring and Grounding: Thoroughly inspect the wiring harnesses for any signs of wear, corrosion, or damage, especially around the connectors related to the TCM, PCM, and BCM. Ensure that all grounds are clean and secured.
TIPM: It’s possible that the Totally Integrated Power Module (TIPM) could be malfunctioning, especially if it’s causing multiple modules to throw U codes. If you suspect this might be the case, examining any visual signs of damage or testing the TIPM itself might be worthwhile.
Battery Voltage: Make sure your battery voltage is within a good range (around 12.4 volts or more) and that your alternator is functioning properly. Low voltage can cause various electronic gremlins.
Codes: You need to tell us what specific codes it's throwing. Use your scanner to do so. Without specific codes we can't be of much help.
Fuse Check: Don’t forget to check all relevant fuses in the fuse box—sometimes, a blown fuse can lead to bizarre electrical problems across multiple systems.
Hopefully, this helps point you in the right direction! Keep us updated on your progress, and good luck diagnosing the issue!