ESC Issue?
 

I've noticed an odd problem with one of my planes recently. It seems I will be flying along and the plane will start to lose power. I apply full throttle to no avail. I then pull the throttle all the way back, then give it full throttle and all is fine and I complete the flight with no further issues. This is not related to any one battery. I have both 15 and 20C 3S packs ranging from 3000 to 4400 mAh. I'm using a CC 60 amp Phoenix and and E-Flite 25 motor. Anyone have any idea what might be causing this? FYI i'm using a separate NiMH battery for the receiver on this plane.