The first step was to build some L hooks that were approximately 12 inches in overall length with a 2 inch hook on the end. In my case I used 3/8 inch rod which was probably over kill, I think 1/4 inch rod would work just fine. Also my hooks had holes in the ends where I installed keepers , but that is only because the scrap rod I used already had the holes. Threading the ends of the rod would work just as well.
The second step was to drill 3/8 inch holes in the top and bottom of the doors frame. The frame is a box construction and the holes go through both sides of the box.
I then used a 2x4 that would reach from the ground to above the top of the door and marked it where each of the holes was and then drilled holes through the 2x4 for the L hooks.
The hooks were then installed through the 2x4 and the keepers put on the ends of the hooks and the whole rig was then set up to the door and the ends of the L hooks inserted in the holes
At this point the jig can be installed and removed in a matter of seconds.
Now a small bottle jack was placed between the 2x4 and the frame at the location where the waste band is located. In most cases on the GMC that is where the door will be bent because it has been let slam open against the coach side when the preventer strap has been removed resulting in the bending of the door. In my case the frame next to the hinge was the only one bent, the other one was just fine after that one was straightened. a piece of soft wood with a kerf cut in it for the lip on the frame extrusion was used to pad the door frame.
Once the jack was in place it was pumped up so it would deflect the door about a 1/4 inch and then released. In my case when the jack was released there was enough tension to keep it in place.
I then marked the door frame and the 2x4 just above the jack and used this as reference points to make measurements.
I then applied the jack to increase the measurement 1/4 inch above the last time and relaxed the jack and measured the result. I started at 12 3/8 inches and went in 1/4 inch increments until I got to 14 before the door took a permanent set that was enough to solve my problem.
This process would allow bending the door in any location desired, and with appropriate padding should be able to be done without removing anything from the door.
As with all my WEB pages this is just what I have done and what you do with this information is up to you. I make no warranties that this will work for anyone else or that it will be as easy as it was for me. If you do use this information use it with caution as you could destroy your door.