[Mark Hamilton]

This sounds like a breaker problem if I ever heard one. Something is causing your motors to stall, causing them to draw far mroe current then normal. Check for side load on the shaft coming out of the motor, that causes stalls very easily. You may just not be geared enough for the tracks you are using. Also, as far as the breakers go, any breaker is more likely to trip when they are "hot". A breaker that has tripped or repeatedly been pushed to near tripping without being given cool down time will trip much easier.