As has been said -- brake please! Or just increase the braking effect of reversing direction (forward or back). And yeah, the turning radius could be tighter. It's also hard to tell the front of the cab from the back -- so when I went sailing though the drop zone off the top of the map (it would be nice to have indicator arrows for those too, BTW) and got returned onto the map facing the OTHER way, it was a little hard to figure out what had happened.
Plus the time limit thing -- longer or extensions based on something, but since you mention power ups that's probably what you're thinking. Nice job, though.