In the scene where there is twin twisters, whilst the they driving between two lakes on a dirt road. Just after the cow flies past. The road ahead shows that it is only one car width and a dirt track. In another, where the shot is into the car, a car passes them in the opposite direction, on the R/H side...!
It happens a few times during the sequence with the "sister" tornado...every time they flip to view inside the truck, you can tell they are on a different road.
Yes, there are a lot of mess-ups or "slip-ups" in this movie, esspecially about this truck, but there is one thing that they do get right. Sometime in the beginning of the movie the right/passenger side of the truck bed get bent in. This stays there the whole movie.