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I've done this pretty much every time I've driven off pavement. It helps if you remove the tail light. Pull the cover inside the cargo area to get to the two nuts. You need a 10mm deep socket to get them off (don't drop them!). Yank hard on the light to pop it out. Remove all the screws and clips in the wheel well. Now.... this part is important because it will keep things from going back together.... I don't know what year your truck is, but on the early 5th gens there is a terribly flimsy metal bracket holding the bottom of the bumper at the back. Get under there to see if there's one. It attaches to the frame and your bumper if it's there. This bracket will keep your bumper from snapping back into place. Remove the bracket and either; A. Throw it out, or B. Straighten it back out and put it back on the truck. After you do that, pull the bumper off just on the edge (where it sits in the body). Look at the long black clip. If any part of it is broken you may not get it seated correctly. Now look below where your tail light was. There's another plastic clip there. It may also be broken. This shouldn't matter. Now start below where the tail light was and carefully press the edge back into the clip using some well placed firm pushes. You should be good. Put all your screws/clips back in the wheel well and put your tail light back in. Good as new. But.... it will probably happen again.
