Update to the update - I think I may need to post a less wordy - less confusing summary, maybe a new thread of what's been done, where I'm at.

Stuck in park - repaired / refurbished RCM (with traction control relay replaced) is now in the car. It will not shift from park unless I override it with a tool through the slot. The shift indicator on the display does show P for park. If I override it, all shifter positions are displayed correctly. Once in Drive, I cannot put it back into reverse without shutting the car off and trying again with override.

Brake pedal switch is new, but I did not have it installed when I replaced the RCM and started the car. Generic code scanner was throwing a P0600 No comm with CAN bus. Is there an interlock solenoid under the hood, or is it at the shifter?

Thanks all!