Make sure you are using the right emissions diagram for the model of your truck.
What is the GVWR of your truck (its on the data plate inside the driver's door). Its probably a 1/2 ton with standard emissions, but if its a 3/4 ton with a GVWR over about 8000 lbs the emissions may be different. Make sure you are using the right emissions diagram for your truck.
My '75 is a camper special with 8200 GVWR, and the factory emissions are fairly simple. All I have is a fuel vapor recovery tank, with no EGR and no catalytic converters from the factory.