My 2008 Terry had a 13' slide for the sofa and dinette and it ran on a rack and pinion system. If you look under the outside of the slide at the end of the steel racks where they meet the outside wall, you will see some adjustments. One threaded rod runs parallel to the floor and adjusts in/out to correct the problem to show. If both sides meet the wall but the top is tipped out, there is a vertical bolt and jam nut that adjusts that. Raising it will tip the top of the slide in.
I got into all this when I replaced the rotting floor in the slide out, so it's possible there is rot either in the slide itself or the frame of the camper where the slide attaches. I had a bunch of pics of that repair but can't find where I filed them....