I have a Torque 2818/900 motor powered with an Airboss 35amp ESC and a Flightpower 2170mAh 25c 3 cell lipo. I have this in a EF Edge 540T. I have noticed that flight times for some reason seem incredibly short like less than 6 minutes flying some imac and 3D. This doesn't worry me too much, but a new behavior does. When I first take off the vertical is unlimited, but after 3 minutes or so the vertical is still good but suddenly the motor cuts out (not totally just lowers to idle for just a second or two) and then picks up again and then repeats the process. I have tried to get it to do the same in horizontal flight, but it does not. It is acting like it is taking too much voltage and the ESC is cutting off and then picks back up, but what would cause this? The motor seems to spin freely and does not seem to be binding at all. This is the recommended setup from EF, so what might be the problem?

Any help would be great. Thanks.