Newer trucks have a self adjusting slave cylinder.
With older ones, it's easy to check. Just check for a little freeplay between the clutch fork and the slave's piston pin with the spring removed. No-play, shorten the rod.
For the clutch, go up a hill in 4th or 5th and floor it. If the engine rpms go up, without a corresponding speed increase, you need a new clutch......
