the reason why you can powerbrake is cause your rear brakes dont work as good as your front its made that way so when you slam on the brakes the assend of the truck dos not come around and spin you out
you use a line lock. you can get them from summit.
its a valve mounted in the brake line with an electic solenoid to control it. you step on teh brake pedal to put pressure on all 4 wheels, then hit the switch to the valve. it closes the valve locking the pressure to the front wheels only. then you let off the pedal and pressure is released from the back, but is locked in the front due to the valve. smoke em for days