I am not at all sure there is a relationship, sometimes trucks just fail, especially when they get older. [I say that the older parts get jealous of the newer parts]. is it when they put it in gear, or when they rev the motor, since the gov. works in relation to motor speed and amount of air going through the throttle throat, and not the motion of the truck. if it is related to the truck motion, I would be checking the wiring to to coil.