It's been quite a while since I drove one of these so I'm not entirely positive but I believe you have to hit reverse twice when you go from forward to reverse. Does your controller have Servo reverse for the throttle channel? If it does, I think I might try reversing the servo and see if that makes the transition from forward to reverse any smoother, and if it does you would then just have to reverse the polarity at the motor. But, that's only if you can reverse the throttle channel. Some video of how it's acting would be a great help.