Brake Problem

[special-K]

I have an issue with the brakes on my '71 C/30. They don't seem to be releasing at all four corners.
A little history:
I bought the truck in '06 and it had just had brakes done. I'm guessing it was just shoes and pads that he called new brakes. The truck has a cab from a C/10 and that is the booster and,I assume,master cylinder/proportioning valve it has. I have hardly driven the truck,but up and down the road a bit. The brakes have operated fine,except the pedal stays down to where if you don't pull it up the brake lights stay on. That's probably just a weak return spring. It needed a starter,then battery,then a carb rebuild due to not being started so long. Now that it's up and running the brakes seem to be sticking.
I noticed in my driveway it seemed to not want to roll. The e-brake doesn't work,so it wasn't that. Going up the road I can tell it's held back and it won't even pull 4th gear (with 5.13s). The brakes are definitely sticking. I figured maybe a caliper or both got sticky sitting. I went about a mile up the road thinking maybe they'd free up. I figured I'd see which hub was hot and tear into it. But,it's all four. I suspected the wrong booster/master cyl/prop valve,but why did it work before and what would sitting do to affect that?
Just looking for suggestions. Has anyone experienced something like this before? I suspect it's up top on the brakes since it's all four wheels at once.