If it's an OEM caliper on the truck now, it probably has a ceramic piston.
Those pistons have a tendency to develop hairline cracks in them and seize. If it's gotten hot to the point of smoking, but exercising the caliper freed it up, it's take it as a warning and just replace the damned thing.
Be careful when buying a caliper, have your VIN handy.
If there's anything more important than my ego around here I want it found and shot!