2003 Chevy Silverado Rear brakes hanging up

Make sure that the parking brake shoes are adjusted properly (cranked in) and did you lubricate your pivot pins on the caliper? Otherwise, it may be a piece of foreign material in the "T" junction block on the rear axle (when the pads rub on the rotor and heat up the fluid, the obstruction is not letting the fluid expand past the junction. As more heat builds up, the harder the pads will push on the rotors).