^^^^ Those are only a couple of possibilities. Get under the dash and work the pedal. If the pushrod only moves a little bit, then it's one of the above (pedal box bushings, bushing/linkage on pushrod eyelet). If the pushrod moves all/most of the way, then the problem is "downstream". Now get under the truck and have an assistant work the pedal. Measure the fork travel; it should be at least 1/2" to 9/16". If it is less, then hydraulics are bad. If it's at least the minimum, then the problem is further "downstream" - bent/cracked fork, throwout bearing issue, weak pressure plate fingers.
Usually if the pedal stays at the floor, it's hydraulics or the mechanical bits in the cab.