I have had a 2 instances of the engine starting to shake when at a stop light. Only happened twice and only for a couple seconds then cleared up. Tonight while going to get something to eat the damn thing started and was clearly not running on all 6. Just as if it had a TOTAL missfire. Ran that way for about 3/4 of a mile and then cleared up. Never once set any MIL lights and after dinner it started and ran fine all the way home. Only have 550 miles on it and the only mod that I have done is 5 inch exhaust turbo back. I have asked a couple techs that I work with and the first time it happened I was just below 1/8th tank and they thought maybe it was sucking a bit of air but now it is full. Any suggestions?