Ok, well, i got my GT back from the shop a few days ago. It was running perfect. one thing i noticed is that around 3k rpm steady, it'll kinda like kick and buck. wouldnt keep a steady speed. but yesterday, i noticed a little clicking which sounded like a loose rocker arm. thats no big deal. But then, getting home it started to backfire. It was pretty bad. any ideas of what could be wrong?