While the electrical tape method might temporarily correct the issue, it will eventually wear out and you'll be faced with the same (if not worse) problem. The answer is, as MudFly attempted, is to adjust the plastic tailgate guides. In his case, he only had to adjust the frame guide up 1/8 inch. You may also have to tighten, or adjust, the corresponding pastic guide on the tailgate door itself. I know it's a pain, but a little trial and effort may be necessary.