1988 gmc c1500 right front brake pad does not release,why?

Rubber hose going to caliper. They tend to collapse internally with age. It will look good on the outside but obstructs the fluid from releasing pressure off of the caliper. With brake locked up remove the hose from the caliper. If brakes then release replace the hose.

open the bleeder on that caliper that's sticking if it releases that wheel its definatly the hose if not its probably the caliper.