I just ran pocono this weekend.Just installed a fresh motor,sohc.Fired right up in the shop,let it run in for a while. I figured everything was good. All I got was two laps then the motor started to missfire and loose power. This happened at about 5,000rpm. Poped the hood found a vaccum line off at the throttle body. I put it back on and it fired up and ran fine. Went back put for the race and it did the same thing again. I talked to my mechanic and he said that it could be the speed sensor. Possibly making the car thinking it was going a million miles an hour and that the speed limiter should cut in. So i changed that and the pcm, Car did the same thing again. Anyone have an idea.