If it has a clutch brake in it, it should only be pushed to the floor when sitting still. If it was pushed to the floor while in motion, the clutch brake is more than likely toast. All non-synchronized transmissions will grind while attempting to put in gear when sitting still, that's just the way it is. Clutch adjustment usually is accessable from an access plate on the bell housing where you rotate the adjustment clockwise or counter-clockwise with a prybar to get the desired free-play in the pedal. You want about 1 1/2 inches of freeplay at the top of the pedal. If the clutch engages about 6 inches from the floor, that's about right. Every individual truck is going to be a little bit different from another. Hope this helps, as I'm not familiar with what truck you may have.