I have 2007. The rear brakes have 2 slide bolts with 2 accordian boots over them. I think the 2003 is the same.
Dirt and mud would have a tough time blocking the movement of the caliper. Also, the brake pads do NOT move with the caliper. The pads move on the caliper mount independant of the caliper. The caliper pushes on the pads and slides on the 2 slide bolts in a different rate and distance on the caliper stand. A lot of people that do the first rear brake change, find the stainless steel "anti rattle" clips a problem with the new pads and throw them out. This allows the steel pads backing plate to dig into the soft cast iron caliper stand and lock the pad into place (very common with the outside pad). Check your caliper stands. The top mount support for the brake pad is going to be "dug out" by the pads backing plate, causing the pad to stop moving and making the piston side pad fail real fast.
If this is true for your truck, you need to replace the caliper stands, install the "anti rattle" clips ( the clips are more like a cover for the brake pad mounting surface, on the calper mount, and prevent the pads backing plate from digging into the mount), the calipers (because they have been pushing on the pads unevenly stressing the seals and pistons. This will cause the pistons to stick and the new piston side pad to fail even faster), the harware and the pads. I have used all kinds of pads over the years, the Mopar pads are the best fit and the best for stopping. You get what you pay for.