I've mentioned it in other threads, but the parking brakes began hanging up on my 2017 Ram 1500 months back with barely two winters on the truck and about 40K miles on the ODO. I was able to free them up externally at the time and I let them be until today when I did a brake job on the rear.
Not the best pics, but the rusty block looking assembly is the part of the P-brake mechanism for the right rear wheel. It's mounted on the bottom on the rear left wheel. You can see how rusty all the bits are in there. Everything is wet with PB Blaster in the pics.
When you mash the parking brake pedal, a lever arm through the backing plate actuates a cam that spreads that block open, pushing the shoes against the drum. Spring tension with the spring you see should retract the shoes. When everything jambs up with rust, the shoes won't retract and you'll notice your parking brake cable sagging.
I got all the rust out I could, PB blastered the heck out of all the metal/metal contacts I could get at and then slathered the mechanism with brake grease. They're working for now, but any fellow rust-belters might want to check this area and apply grease before things get expensive.