You can check the cable easily enough. Have someone sit in the truck and depress the clutch pedal while you watch the clutch lever on the side of the transmission. If the lever moves back and forth, the cable is still connected. If it does not move then the cable or one of the parts that connect it has failed. If the cable does pull the lever, then you have a more serious problem that will probably require the transmission to be pulled from the vehicle. It could be the release fork or the release bearing, or the clutch its self that has just worn out.