GMC Sierra parking brakes?

If it is a late model, there is a c shaped brake pad inside the rear brake drum/rotor. Pull the tire off, remove the disc brake caliper, and remove the hub. There you'll find the c shaped parking brake pad. Pry it off the top cam. There is a small clip at the bottom inside of the pad.held on by a hex head screw. It's a relatively easy job. Check the hub for wear. I had 1 side that wore due to constant pressure on the pad to hub so I had to buy a new hub/rotor. The cam can be adjusted much like the older style brake pads. A mech told me this a common occurrence due to poor design. The pads come 1 to a box. Mine ran @ $45.00. Good luck.