Rear Brakes Frozen

[DreamRyder1963]

Tonight as I was trying to leave work I found that my truck would not move forward. It seems that rear brake locked up while I was at work. We were able to push the truck forward and then move it into the space in reverse with no problems. At that point the truck would move forward under its own power but it was still being held back. We repeated this process several times and it got better but never let go all the way. It has done something similar before but the truck was never fully stuck and it quit after a 100ft or so. Is it possible that actually frozen up inside the drum? I ask because itonly does this when it is sitting for a couple of hours and it is always with a cold snap.