This guy should consider trying a different dealership service dept?.
It'd be surprising if GM Head Office hasn't suggested the vehicle be sent elsewhere already?.
In my car business days I often found customers like this guy were just overfrustrated good guys that'd had the royal dickaround by a dealer w/ internal problems...usually a cheapskate dealer principal combined w/ the resulting weak service personnel training and techs who'd spent time building their attitudes instead of skills?.
Fix this vehicle's bad ground or whatever problem it really has and you've got a customer for life!.
I like the lemons on the bumper touch too!
~ Pete