Be careful at Nabors. I bought my platinum V there, but I wont let them work on it. They could not tell the difference between a bad water pump and a radiator (the mechanic could, but the service writer could not). I have had trouble with rent cars, problems with getting things fixed the first time.
Patrick at the Pontiac/GMC dealer in the Tustin auto center has some mechanics who know what they are doing on the LS6 and the rest of the car.
Nabors wants to give you free oil changes, but sometimes free is not worth it. 1st oil change even I had trouble. Just a word of caution.