You're very welcome. Driveability shops have technicians with strong diagnosis abilities in problems like you're experiencing. Hesitation, stalling, no starts, computer control problems.... The hard part is getting the vehicle to act up when the tech is looking at data on a scan tool. Vehicles that don't set codes are the hardest. Your tech did the right thing by recommending a service with the understanding this might not be the cure.
I have a couple of suggestions for them to look at. The link below is a service bulletin from GM concerning a hesitation problem that maybe useful.
1. TSB - PI0090A Intermittent engine hesitation or flutter without Diagnostic Trouble Code (DTC) (inspect and correct intake camshaft position (CMP) sensor bank 1 connector terminals for intermittent conditions or poor connections).
2. Check and make sure there is no oil getting into the air intake system and contaminating the mass air flow sensor. If so GM has released an updated PCV tube and camshaft cover to correct this condition.
There were a couple more issues I've noticed with this vehicle, but there were DTC's present, where you have none.
I hope this information is helpful. If you or your technician have any questions or run into any problems let me know.
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