As mentioned above, pull the drums and have someone apply the parking brake and the brakes (Only 1/4 of the way to avoid popping the wheel cylinders) a couple of times. See if everything is moving freely and releasing all the way. See if everything is in the correct place. (That the e-brake arm, tension wire, and spring have not come off, etc.) If not moving freely pull everything apart, clean the backing plate, the shoe edge, and all the parts and pieces. (Use Brake Cleaner) Then lube appropriately and re-install. With a big screwdriver (Or a $12 brake adjustment tool from your parts store.) you can spin the star adjuster inside the drum area via the little window at the bottom of the brake backing plate. (There is supposed to be a rubber plug in the hole, yours may be gone.) Turn the drum as you turn the star to determine if you are tightening or losing it. Once you loosen it some, the drum will come off. (May need to tap with a mini sledge to break the drum free of the axle as they can rust to each other. Don't smash it or damage it, but it may take a good couple of hits to vibrate the rust apart.)
1) As several have suggested it could be the e-brake cables are sticking.
2) It could be the lever that the e-brake cable pulls are rusty or the pin that holds it is binding making it stick. So you release the brake in the truck, the cable slacks, but the e-brake arm does not release all the way and drags. As mentioned above and likely more common is rusty e-brake cables. But a clear view and access to the e-brake arm and cable will help you determine what is actually wrong.
3) It could be a bad wheel cylinder. (Dirt, rust, or worn inside and sticking.)
4) It could be a master cylinder going bad/sticking, not retracting and releasing the pressure.
5) It could be you have something loose in the drum. (Piece of brake shoe, a piece of rust, too much brake dust, or something metal has come loose.)
6) As mentioned in another post recently I was in, a ballooned/swollen brake line could be to blame. Brake lines are able to balloon/swell, so the pressure from the master cylinder is enough to squeeze the brake fluid past, but once the pressure bleeds down, the remaining fluid is stuck and still pressurized. Long shot but worthy of consideration.
7) As mentioned above, a bad brake differential valve. You learn something new every day!
8) Clogged or pinched brake line.
For the member who recently replaced his brakes, and they are tightening when not intended.
1) Make sure you put the correct parts on the correct side. As I recall you cannot put the shoe star adjusters on the opposite side. They also only go in one direction, but you can mistakenly reverse it. (I usually take a pic or two, do one side at a time, then can refer to the other side. Not suggesting you did it wrong, but the issue calls for inspection.)
2) Pull the drum, have someone work the brakes and the e-brake. Make sure everything is working as it should. Then you will know to look at some of the items above.
