Engine Performance problem
2007 Chevy Equinox 6 cyl Front Wheel Drive Automatic 28,500 miles
After I lost my gas cap, probably a couple of days, I went to the chevrolet dealer and bought a new one. A tech told me my engine lt. Would go on but after a couple of days it would go off. It took a few days but my engine light didn't go off so I took it in. The tech noticed how loose my gas cap fit and rec. I buy a new one. So I took it back and the tech said it wasn't the right model and I exchanged it for the right one(I hope). My engine light did not go off for 2 wks and I noticed how jerky it was as the car shifted gears(manual), especially at 40mph. It seemed like it would stall out. I have always had the oil changed when the message lights go on(maintenance I and II). The dealer checked the computer and it was fine but the car still jerks like crazy. Dealer said maybe a bad batch of gas. One tank of Shell gas later and I don't see any improvement. What do you think is wrong? What should I do?