Look at the crankshaft timing...
Look at the crankshaft timing scale to see if port closure occurs at the proper amount of degrees. If not, the cover shown in the photo needs to be removed to gain access to the pump drive flange and bolts.
If the pump timing is found to be wrong, remove the accessory drive cover plate. To do so, loosen and remove the fasteners that connect the pump drive gear to the pump drive plate. With a breaker bar on the crankshaft bolt, turn the crank to the port closure specification. By uncoupling the pump drive plate from the pump drive gear, the pump will remain stationary at port closure on the #1 cylinder while you turn the crankshaft. When the engine is in the correct position, torque the fasteners that couple the pump drive gear to the pump drive plate. Turn the engine backward approximately 20 degrees before the port closure timing specification and then recheck the setting.
The timing test procedure is not complicated, but may be difficult to perform with the engine in the truck, especially if the vehicle is raised up or has big tires. Do not become frustrated. You will most likely have to go through the steps two or three times before you feel comfortable the values you obtained are accurate.