[eippermx]

I'd recommend the first thing for you to do is retrieve the codes. By retrieving the codes, you will have a starting point to determine why your computer is not happy with the way your vehicle is running.
If you do not have an Autozone or similar retail parts store that can do it for free, take your car to a dealer or local mechanic. Or buy a scanner for $100 bucks. Wal-Mart sells 'em.
In your case, if I was in your shoes I might get an independent point of view. If you don't buy the scanner, consider paying for the diagnostic so you don't wind up paying for unneeded parts and labor.
In my case, I take my cars to the GM dealer when I can't figure out a problem. I'd prefer to pay the extra $$$ for trained GM techs to diagnose my car instead of a local mechanic guy who "learns" on my vehicle.
Post the codes here in the forum and you'll get some good info/advice from very knowledgable members as to what's happening with your car.