You need to turn
on the freewheel option and turn
off the drag brake option. Mine did the same thing when I first set it up. Make these changes and it will drive just like the other controllers you are used to. Another recommendation I would make is to set it to CAR forward only. The reverse brake thing is still a little funky on these controllers even though it is worlds better than it used to be.
Sweet truck by the way. You should be able to win a few races with that instrument.