Originally Posted by Dave H

You mentioned full throttle and the steering starts acting up. The left turn issue you describe, are you turning full left on the radio, possibly with full throttle also? What about partial throttle and steering, is it OK then?

My WAG: Have you set the servo endpoints correctly? It’s possible the endpoints are set too high, at full input the servos might be binding up and causing problems. Granted one would expect this problem to occur with the motor off as well, but perhaps they are right on the edge, motor vibration and/or any flexing under load then contributes.