Chances are good that if your rotor was warped it would spin easily and then get hard as it reached the warped area. It sounds like either the caliper pistons are sticking or something is not letting pressure release from the caliper. Best thing to do if the pistons are sticking is to replace the caliper with a new or rebuilt unit. If pressure is not releasing it could be caused by a bad brake hose to the wheel. It may look ok externally but have internal damage that makes it act almost like a check valve. Lastly, I'm not familiar with the brakes used on the solid axle trucks only the IFS, but how do the pads mount? Are the in grooves on the caliper bracket or are they held in with pins through the caliper? If they fit into grooves you may want the remove the pads and clean these areas out with a wire brush and file. Also if the caliper mounts on slide pins rather than bolting on solid one of these could be sticking. Hope I can be of some assistance to you.
Andrew
