I have a 2005 crew cab 1500 2WD. The parking brake pedal goes to the floor and won't come back. I looked under the truck and there is a lot of slack in the brake cable, like about 6 inches. I have drum rear brakes. The rear brake shoes have about 15k miles on them. The cable goes around the cam on the parking brake pedal and looks like it should. Both cables to the wheels from the equalizer are the same length. What could be the problem?