Where did you get the clutch and pressure plate from? There are alot of different style and designs of clutches that produce different performances and it can completely change how the truck drives.

Is there any sign of the slave or master cylinder leaking? Alot of times the extra stress placed on the master and slave when the clutch is nearing the end of the its life will kill seals and not provide enough pressure to work the clutch correctly, It may work, just ot how its supposed too.