I have 2005 base Grand Prix with 3.8 that has 225k miles on it. For bout 8-9 months when I start it sometimes it will have a miss in it. But if I turn it off then start it again the miss will be gone? Thought that I might have sum trash in the tank but I also am leaking sum anti-freeze somewhere on the backside of the motor by the firewall. I figured if it was a head gasket it would have already blown.... Car don't run hot just gotta put bout a gallon in it bout every month. Any suggestions?