GMC Troubleshooting Questions? Ask a Mechanic for Answers
I am sorry that you have not been helped yet. I just came online and saw your question
This last time it was in to the dealer, did they retrieve and faulty codes and if so, what were they?
Also, the last 8 digits of the vin number is ***** to pull up any schematics I might need to reference as well as check of any service bulletins or possible software updates.