I have a 1992 Mercury Grand Marquis. Once in a while the brakes seem to just hang up. I've replaced the power booster, the calipers, bled the brake lines, checked the master cylinder, but have not done the proportioning valve yet.
I can loosen them up again if I lift the brake pedal with my foot while I'm driving. Have you seen or heard of a similar problem in the Ford line or any other cars? I'm gonna pull my hair out and get a horse if I can't resolve this one.
The problem you are describing is in sync with Ford Technical Service Bulletin number 92-19-2 which I located using the ALLDATA information system. This bulletin pertains only to vehicles equipped with Anti-Lock brakes, and describes a slow or lack of brake pedal return which can produce an unwanted brake drag.
The cause of the problem is the power brake booster which can be corrected with the installation of an updated version (part # F1VY-2005-B). I know that you have already replaced the booster, but if you purchased a used or remanufactured part it may still be the cause.
So the first thing to do is confirm that the unit you have installed is the correct upgrade. Aside from that, the fact that the brakes release when you pull up on the brake pedal leads me to believe that the problem is right there at your foot. Possible trouble spots are the pedal assembly binding, an oddball condition with the master cylinder, or, again, the brake booster.