Those trucks are well known for the rear brakes getting rusty and having to be replaced, not cause they were worn out, but because the rotors were just too rusty. Happened on my 04 2500HD and my dads 2500HD. But this usually causes a lack of braking, not excessive. Your truck should also have the AAM/GM corp 10.5" full floater axle. These are also known for leaking rear hub seals (also too familiar with this repair) and that oil could have soaked the pads which will cause sticky brakes.
Sounds to me like you should plan on replacing rear pads, rotors, rear parking shoes and hardware and doing the hub seals and the small paper gasket at the end of the axle shaft to the FF hub. I wouldn't trust Midas to look at it for you, they're like the fast food of brake repairs, sure it's cheap but you'll regret it later.
Also watch for, where the pads slide on the caliper bracket, there is a stainless shim that they slide on. If you want, that can be cleaned up and reused, unless you get the good pads (highly recommend) that come with new ones. BUT, where those shims clip on to the caliper bracket will rust and expand under the shims and lock the pads in place (again, familiar with this too). I had to use a hammer and chisel to knock down all the loose, flaky rust so the pads would slide properly again. Do yourself a favor and put on some glasses when you do this. Rust specs in your eye are bad.
