WX, to do that, you first need to remove the seat belt hangers (large nut), and the sealt belt anchors (large allen screw which might be hidden by some trim). The rear panels come off by pulling straight back (not up, like the front panels). However, there are about 10-12 of those "push-pin" type of fasteners that secure the panel to the door. So you will want to slide a small, flat pry-bar of some sort between the panel and door where the pins are so that you can apply outward presssure on the panels in the areas where the pins are. This is so you don't crack the panel in those areas, or break the pins.
I did mine about a month ago to install new speakers.
I probably didn't do it the right way but didn't break anything.
I just removed the seat-belt nuts like Rockledge said and then just pulled the panel as hard as I could.
Hmm.. Yeah that's what I did the first time. I unbolted the seatbelt and used a tool to pry outward on the panel all the way around. But I broke the panel on one side, and broke a push-rivet on the other side. So I was just wondering if there was a special tool I SHOULD have to do this with. Sounds like I'm doing it right...it's just annoying. I wish the speakers were simple to get to on these like they are on the 2-door Supercab. Thanks for the response guys.