Brake caliper

Are you sure the caliper is sticking? Does the truck pull to the left when you step on the brake? If so try checking you air pressure in your tires and then rotating the tires front to back. A broken cord or low air pressure can cause a vehicle to pull as if a caliper were sticking. Since you changed the caliper and it continues you may also want to change the pads and cut the rotors to ensure they turn true.