We had a very similar experience with the GenII in my sons buggy, drove me nuts, cost him a couple of races in stock buggy, he would slap coming off one of the jumps and the would just die. I would get it from the marshall and it would be on and work just fine. Ended up being on of the leads on the stator was loose so when he slapped the motor would lose connection and not work, when I picked it up and moved all the wires it would work again. Since getting new motors we have not had this happen again, so maybe you could check that out on your car as well.