[RayChez1]

Dave, it sounds to me like you have a bad air leak in the emergency line which does not allow the pressure to be over 60 lbs to push against the springs which release the parking brake, which is on the rear only. And if you do not have an air leak, you have a restriction somewhere between the parking brake button which opens up the air flow to the valves on the rear which allows the springs to release.

How is your air dryer? The air dryer should be changed out at least once a year. If that filter gets plugged up, it could be problematic with your air brakes.