What could cause intermittent smoke from the rear drums?

What is your question?

I just bought a Bronco a few days ago. Today, I took it to Grease Monkey to get her up to speed to pass emissions. When I go to pull out, the parking brake is on. I release it. Just after I get done with emissions, both rear brakes start smoking. I'm wondering what the probable cause of this issue is. The brake fluid is topped off, and steady. The Pedal feel will go between rock hard and spongy. The brakes will grab so hard that I can't move out of a parking space, then after they cool, it will be hard to move from the space, then be ok for a while. I'm hoping that it's the parking brake so I can just unhook it.