well it has to do with interference. the ESC runs on the same frequency or the magnets interfer (somthing like that). when i drive my car it kind of glitches. i can drive about 15 ft away and it goes WOT on me and it just takes off. so i tried it with my friends AM and the same thing happened. Then a guy at my LHS with the same setup told me to get FM, it preforms better and i will get better range. Does your son have any problems with glitching or it goin WOT on him?