JAW's
B/W Country & Amer. R&R
My first guess would be a severely worn drum... To the point of being grooved. Like the brake shoe is going up inside said groove and getting stuck there. But no way to Tell for sure until you pull that bad boy apart.
Sent from the big block!
I'm leaning towards a seized wheel cylinder. I've seen it before on a k1500. Rear wheel seized as my coworker was bringing it into the building, the truck jerked sideways into the bay door suddenly and wiped out the fender flare.
Working the e brake back and forth might be enough to get the wheel cylinder pistons to retract slightly so that it frees up.
Also the lining may have broken free of the brake shoe and now there could be chunks floating around inside the drum, seen that too. That's why I avoid bonded shoes and buy riveted when possible.
Just throwing ideas at you bases on some experience. You'll have to pull it apart and give it a good inspection.
Good luck. Let us know what you find.
Thanks for the ideas guys. I'll be sure to let you know what I find out. Hopefully something simple.