RE: Motor or ESC problem?
If your system is shutting down at 60% throttle that indicates you are drawing more than the batteries can deliver... and hitting LVC. If you continue this way you will ruin your packs (and maybe the motor unless it can cope with the 100A or more you must be drawing....that motor is rated for 65A max.)... you need to get a Wattmeter on it to measure the voltage under load and amp draw.