and it seems to me, it would be considerably difficult for an A/C truck to wind up with "shoot through" causing full battery voltage like a DC truck (ala PMT) since the motors work considerably differently. I would greatly doubt the controller failure, and more expect this to be a problem between the operator presence pedal and the steering hand crank.
I would also doubt that "applying the brakes does not stop it only slows it down" unless you have found at least part of the problem; a (stuck/broken/shorted) brake switch.