Drove from Boston to Naples FL last week. Noticed a slight shaking at idle, but vehicle ran well at highway speed and gas mileage was great. Today the emissions light came on. I called On Star and was told that I had a miss fire but not to worry about it and that it was safe to drive. Stopped at a Chevy dealer a d they scanned a P0302 code and reset the light. I am going to Orlando tomorrow and will fill up with higher octane gas to see if it helps. Anyone else have this problem?