The problem is after a couple laps the tires "tack" up real good, it pushes worst than a 2whl buggy with a 9 turn.
Is it good for a couple of laps, then starts to push or is it bad from the start? A car can push if you get off line (in the marbles) and my take a lap to get the tires clean. A body or chassis rubbing can cause a lack of traction at one end of the car.
I think the best thing to do is ask someone at the track. Your problem is kind of hard to troubleshoot on the net.