you may find its down to thin wires from the battery to the esc? or a poor connector? it it has that little red jst type, your stuffed wanting 17 amps through it. try runnoing the motor below the cutout speed for a couple of mins and check the temperature of the wires? if they are on the hot side of warm they are not heavy enough. i had a similar problem with an over propped shocky on 3 cells lipo. i programmed my esc to 2.7 volts per cell instead of 3, works ok and the batteries are still good.