If your truck is a quad cab (98+) with the 4 doors. The process is really simple.
Grab your shut rear door (with the front door open) and push/pull on it to see if there is play in it. If so, this procedure should fix your problem, if not, I don't know what to tell you.
Get a T-40 torx bit, the striker that is on the rocker panel that the rear door latches to (It's basically an upside down U) take the 2 torx bolts and losen them up (you do NOT have to take them all the way out, I don't think you should, I'm guessing there is some kind of square nut in a channel on the bottom of them, so you dont want the nut to drop into the rocker panel) Just loosen them up and tap on the striker (inwards towards the cab of the truck) about 1/4 of an inch, tighten the 2 torx bolts back up and walla!
Takes a grand total of about 3 minutes, and that was including the time that it took me to look around the garage for the right size torx bit.