Call me stupid. I keep reading your question and don't understand what you are asking. Are you wanting to reverse servo direction from the transmitter that you said you can see the servo reversing switch on?? Or are you wanting to shift the vehical into reverse? To shift into reverse the tranny has to have the reverse gear module and 3rd servo. To controll the 3rd servo with a 2 channel radio the truck has to have a 3rd ch controll chip. When you hold the brake for so long then 3 will shift to rev. Hold brake again to shift back to forward.

Let me know if you need any of these components. I have some spare parts to get rid of