Not a roll pan or a splash apron. The part is called a rock guard and they were available from the factory. They lay on top of the bumper brackets of the factory bumper that looks like this:
Chrome Rear Bumper With Rock Guards They are similar on the stepside bed, but they are tapered a little from left to right.
If you look real close at the photo, you can see them on either side near each end of the bumper on top of the bumper brackets.
Tony
