My gtb runs excellent with my 13.5 but when I use a 4.5 or 6.5 it has very limited range before it glitches. Same thing with mod brushed motors as well. My power cap has a dent in it so do you think that the higher powered motors are drawing to much power causing it to glitch and the 13.5 being a lower powered motor runs fine??? So basically I think the cap is shorted.