I wouldn't say intermittent ground I would say making bad contact with the module itself. Good to deoxit and insert/remove multiple times to clean up. For folks with more free time use a fiberglass cleaning pen.

Check the rear light cluster contacts. I have had a few burnt bulb contacts which could well cause shorts back down the line.

Worth checking these relay too now it has been highlighted. Thanks for letting us know!

Neil.

while I do not have a old TCM dump, it really is down to 1 byte configuration change to disable Neutral Control.

You change one byte from a 1 to a 0. And that is it. The problem of course is flashing it.