The 55 has been running good all month. Pulled it out the garage today and did not let it warm up like uual. after a mile or so the car started to misfire. I pulled over to see if I had a spark plug wire off and nothing. I drove the car on the highway and at high rpm it did not misfire at the stop light as I cam to a stop it was barely idling. I just tuned the car up and don't know what it could be.