If the brakes are frozen, you wont be able to move the wheel at all. One wheel may be frozen, or both could be frozen. If a wheel spins a few degress and then locks up, you probably have some rear end problems. You might try backing off the brakes and rock the truck with a tow chain attached to another truck. The jarring would probably brake the drums loose. I have also heated the drums with a torch and hit them with a sledge hammer a few times. I try not to do that method if possible. I'm always afraid that I am warping the drum by beating on them.