Well, until then, try this:
From page 6 of
the manual, the forward-most switch near the steering wheel is the CH3 switch, and is default to linear mode. Linear travel is where the servo moves only as long as the button is held down. Don't know if you want this, or latched operation where the button press puts activates reverse until it is pushed again and returns to forward gear.
Page 29 explains how to reprogram the switch to "Aux 2P", which is probably what you want. "Aux 3P" would be if you had some type of tranny where there were three gear positions. You don't want this. While you're there, you can even reprogram those three switches to be different if you want.
Then, it should just be a matter of adjusting the EPA and trim settings of CH3 to get the servo to move like you want.
Be careful though. The reverse gears in the Revo are notoriously weak. If the truck is still rolling even a little when you engage reverse, you will most likely strip the gears. This is why the Optidrive is there; to prevent reverse from being engaged until the truck is stopped.
If you insist on keeping this type of reverse and strip the gears, I believe Robinson Racing has the steel version of these gears. Even then, it's not healthy to be switching between F and R while in motion.
Hope this helped even though I have no idea what I'm talking about!