Problem with Motor and Servo configuration with ArduRover 4.0

I’m using Ardupilot with skid steering rover I assume that there is a dead zone in the right motor because the rover turns when it is moving forward
I tried to tune the servo output by changing the trim values so both left and right motors can start moving at the same throttle level but the problem is when I test motor D from mission planner both motors start to spin I expect that the right-motor is the only one that should spin . these are the servo functions config

  • SERVO1_FUNCTION= 73 (Throttle Left)
  • SERVO3_FUNCTION= 74 (Throttle Right)

I appreciate your help with these situations