Trick camera angles during the mountain driving scenes?
One need not be a student of physics to realize that some of those grades were far too steep to haul a huge trailer up, or even a small one, for that matter.
shareYeah in some of those scenes the car and trailer were going up at a 45 degree angle. Must have been done in a studio with a tilted camera and painted backgrounds or back screen projection, probably both.
shareIt was a combination of both location and sound stage with rear projection; in both cases the camera was tilted in some shots to make the grade appear steeper.
Simple but effective.
Poe! You are...avenged!