The scalextric cars it turns out are the issue, specifically, when the cars corner, it's not bad track…power is perfect across the track. It's the wire braid that is losing contact on the corners. If you go fast, it maintains enough contact to keep going. If you go slow, intermittent spots on corners, etc lose contact for a moment. At slow speeds though, that's enough to drop the power to the motor hence car stops.
Solution…faster speeds or replace braids. Guess I'll do the replacement braids in the next day or so..stay posted. Kids learning to race are having it's challenges.