I've only had my '09 g6 gt for 2 months and it only has 38,000 miles on it, but sometimes at a stoplight, the car will chug or rock back and forth for a few seconds and then stop....I thought it might be a dirty injector so i had an injector/fuel service done on the car, but the chug still occurs. Could it be the gas im using (costco gas) or something else? I leave to go to tennessee from florida in a week so id like to get this problem worked out. Any suggestions??