Not sure if this helps, but I had a similar issue with a mr02 chassis, where the screws that hold the metal tabs that make contact to the battery were loose causing intermittent power outs. But you still have steering.
– Take your motor out and see if it runs a single aa battery. Brushes worn down ?
– Check the wiring to the motor and ensure that the tabs are screwed down properly onto the pcb.
– Check Fets for damage.
– Change crystals in tx and rx.
– Ensure tx batteries are fully charged.