bk20120 problem, nd help

I just hooked up my bk20120 and got it programmed. All seemed fine until I ran it for about 1 minute and then the throttle started cutting out when I pulled full throttle. It is acting like it has a voltage cutoff? I am running it on 4s lipos and I tried 2 different packs and both did the same. It will let me drive it slow, but if I pull full throttle it pulses the throttle. Anyone have any idea if this has a voltage cutoff or any other idea what could be wrong?