Got any extra old ballast to swap in to see if the problem goes away.

'03 LCM went south around 50-60K.
It was very obvious thought. Symptoms would be , care was turned off, brake lights if not lows would stay solid on. Etc, etc. Can't recall the other wine notes but it was clearly the LCM at fault.

Chasing a gremlin - which I can't recall, but similar to yours I think.....to be frank, it's been so long, but buying new ballast I do know made the problem go away...