I too have the same problem, which beleive it or not, started to happen on the same day!! (I race with Asimo)
Full throttle on the straight, then for a second no power (still have steering though).. It was only happenening on the straight at first , but then it started to happen more frequently around the track...
I too have a Cap that came with my esc (GM-SX12w), but had been using it for a few weeks without any problems.