The trackstar will burn a justock up in minutes, its only rated down to 13.5 IIRC. The Castle is non-sensored so the Justock will not work properly with it, plus a 3.5 will burn it up faster than a 6.5t will. Go back and get yourself a decent 17.5t motor and install it in the buggy. Keep the ESC you have. It will make for much more enjoyment.

So you were right, he didnt know shit. But you got a great ESC it just has its limitations. a 17.5 or 13.5 would work great with that buggy.