Unless your brakes are dragging loosening the adjusters won't help, the drums are just rusted on. Sometimes there are round clips on the studs to hold the drum to the hub, remove and discard, they are just there to keep things together during assembly. Easy way - jack the entire rear, remove both tires, start the truck and slam on the brakes in forward and reverse, they will come right off. For safety's sake use jack stands and leave one lug nut on loosely to keep the drums from rolling down the street. Hard way - beat on the drum face with a sledge hammer.