Are you sure you want to do this before testing fuel pressure and for air in the fuel? You may have a boost leak in the aftercooler. Could anything else be work with the truck? Is the temperature too high for #1 diesel were you live?
If your set on turning up the fuel you can find the fuel screw between first and second rocker arm group under the valve cover. It usually has a plate held down by a rocker arm bolt. You could back it out one turn. You will need to back out the air/fuel ratio screw also. It is behind the plug on the side of the governor with the triangle shaped recessed area. Back it out on turn but don't turn the stop screw which you will see when you remove the plug. The screw you are looking for is behind the stop screw and just lower than the stop. It may be helpful to plug off the waste gate line from the turbo, it releases excess pressure when too much boost is seen.
WARNING: ALL OF THESE SETTING CAN DAMAGE THE ENGINE.
Too much boost and/or fuel can overheat and lead to shorter engine life. It will also hurt fuel economy.
These are always the last resort steps when nothing else will work!
One more turn will cook your goose! Don't fix it if it ain't broke.
If you like your results and have lost your fuel economy, leave well enough alone. You want to avoid overheating and melting pistons.
Thanks for the accept.