Drum Brakes Sticking

Check the wheel cylinder to see that the pistons inside it move freely and don't hang up with your fingers. If it's not smooth, then you need to replace them.

Or also, have you cleaned and greased the 6 contact spots on the backing plates where the brake shoes ride? They need to be cleaned and a light coat of axle grease on the 6 flat spots on the backing plates so the shoes move freely.

Then, check to make sure that you don't have a pinched brake line that could be restricting the fluid flow (steel or rubber)...