72MHz is not the problem - there are some 2.4GHz snobs out there. 72MHz has worked for longer than most people on this forum have been alive.
Try to get a cheap (like $5) UBEC to separate your motor noise source from your receiver/servo circuitry. Be careful to disconnect the power lead on the throttle connector to the speed controller. The motor current drain could be pulling down the BEC output to the receiver which a separate UBEC will fix.