Here's a quick check- - - -look at the angle the throwout fork makes with the bellhousing. If the right throwout bearing is installed, the angle should be approximately 90 degrees. If the fork is at an oddball angle with the T/O bearing touching the clutch fingers, you've probably got the wrong bearing installed. I've also seen problems with the pivot ball in the bellhousing cause difficulty disengaging the clutch. If the ball is worn or broken, the fork can't get full travel to release the pressure plate. On a truck that size, the 11" or possibly the 12" clutch could be used. Bellhousing clearance and the position of the holes in the flywheel will determine what size will fit best. There should be about 1/2" to 3/4" of free travel at the clutch pedal before the throwout bearing contacts the pressure plate fingers. The bearing should not run all the time, only during shifting.
Edit: It's also possible to install that clutch disc backwards, with the torsion springs against the flywheel bolts. In that case, it's impossible to get the clutch fully released, even with the correct bearing installed!
Jerry