I know this has been mentioned before but it's worth saying again, if you haven't checked your spark plugs for a while I recommend you go do it now! I just checked mine because I realized I had set them wrong the last time. It's been about 30K and all four of them were loose as could be! I mean finger loose! When I changed them before I torqued all four to 20flb. I think GM should put this in the manual as a routine maintenance item......