Also, there is a plastic bushing that goes on the end of the clutch linkage on the pedal end. If that bushing is gone, you are losing some travel, and it can lead to wear elsewhere. About $8 at your dealer for the part.
Slave and master, I'll agree. Pull the seal lip out and check to see if there is fluid in the bore. If there is, there's your issue.
A bad/gone pilot bearing can also cause this problem. I had a cracked clutch hub disc that warped when the clutch was pushed in, and that was my issue. The master and slave were good, the clutch disc and the pilot bearing were bad, causing my issue. Check things out before you throw money at it. Truck parts ain't cheap