You will want to put the box in the air till the load rest against the tail gate with the back of the tuck at your starting point and the and the PTO still engaged put the truck in low and let out the clutch wile tripping the gate. As the rock dissipates slowly raise the box to keep it about 2/3rds the way up the tailgate. Remember if you are rolling too fast and push in the clutch the box stops going up too. It will take a little practice but when you get good at it you can paint a driveway with your truck and it will take very little raking and grade work to get a finished product. In fact the ground you start on will take more prep work than the rock you spread will take finish work.
