It could just need adjusting. block the wheels. engine off. get a helper and crawl underneeth. Look to see if the front cable, is attached to an equalizer, and the 2 rear cables. ( all 3 cables should meet in a Y configuration.)If so, have the helper apply the parking brake while you look at the cable and determine if it is actually moving, (being pulled toward the front of the truck). if it isn't it is broken or dissattached from the parking brake pedal mechanism.
if it is moving,try with channel locks to pull on one then the other rear cables. If you can pull them more than about an inch, they are probably not connected to the shoes inside the drums.
If they move some try to adjust the nut that is on the main cable, that pulls on the rear cables to shorten it. Have your helper push the pedal dowh about 4 or 5 clicks, and tighten the nut and shorten the main cable. You should be able to have a good tension on all the cables by the time you have the nut about half way down the threaded adjuster end of the main cable.
If this still doesn't get you at least some parking brake action, then you need to remove both drums and see what is going on in there.
The cables may be off the actuation lever, the equalizer bar at the top of the shoes may be out or installed improperly, The piviot point on The secondary shoe may be off. Or the entire rear brakes may be assambled incorrect. Get a manual to show the correct assembly, that will point you to what is wrong.
Good Luck
Tell us what you find