Did the shop tell you what they believe the problem might be? What kind of lights are on the car - halogen, or HID? If they're HID lamps, this could apply to your car:
#14823: Special Coverage Adjustment - Daytime Running Lamp Inoperative - (May 12, 2015)
Models: 2007-2012 GMC Acadia Equipped with High-intensity Discharge Headlamps (RPO TVD) Heat generated by the daytime running lamp (DRL) may deform the bulb gasket. This condition could result in the loss of DRL function and cause damage to the headlamp assembly. Dealers are to inspect the headlamp for damage and replace the headlamp assembly as necessary. For headlamps without damage, dealers are to install a new gasket and reinforcement plate between the socket and the reflector. The repairs will be made at no charge to the customer.