Your settings look correct for the transmitter therefore it appears that your servo is drawing too much power and causing the voltage to drop to the receiver. Try adding a "glitchbuster" capacitor to the receiver. I have had to do that with some of the more powerful digital servos. Also check that your steering is not binding anywhere causing the additional draw in power and that the end points are set so that you are not binding the servo at the far end of the travel.