Jack up rear of truck and remove the wheels and brake drums, inspect to see if the shoes are against the top post that the springs are supposed to retract shoes against. If shoes are tight against the center post, more than likely not the emergency brake is released and your dragging is from improperly brakes (dragging). Or perhaps the drums are out of round and need machining. Keep in mind there is always some drag with properly adjusted drum brakes, just as there is some drag on self adjusting front disc brakes.
Get back to us with what you see.