Hi my name isXXXXX
I feel your frustration with this kind of concern. You are correct, the concern is with the Class 2 communication. Unfortunately this is one of the most difficult concerns to Isolate.
Any one of the modules on the class 2 line can be the culprit. You have a good start in going to splice pack 205 , and isolating it down to a BCM or PCM.
Reprograming does not correct a hardware issue with a module witch is usually the case in these matters.
If I were at this point I would check or rerun the communication line to the modules first.
If that did not correct and I did not find a definite short to ground, Next make sure there are no after market devices hooked in any where. Connections to data sources powers and grounds to modules will make them do weird things. But I don't think that is your concern here.
I would replace the BCM they have had more issues than the PCM. Plus the BCM is responsible for the body functions that your having troubles with.
Look around the left inner fender for the most likely spot for the communication line to be shorted that goes to ECM. It is most exposed and I have found allot of problems in that area.
Hope this is the info you were looking for. HAL