Here is a link to the EPA that sketches out the importance of NOx reduction as the interaction of VOCs, NOx and sunlight result in large levels of ground level ozone.
Frequent Questions | Ground-level Ozone Standards Designations | US EPA
Your point about economics being a great part of the equation should hint to readers that early adopted emissions technology is not anywhere near being optimal in attacking the problem. And, like any technology, there are growing pains.
The officials in place at the EPA are not entirely out of step with the common man. They do have open forums to discuss possible changes and laws. I know, I have been part of some of those discussions in the past. I agree with you that CO2 being listed as a "pollutant" is an undue burden to industry, but I and others got to have our say in the matter. The problem was, the scientist and engineers such as myself, were far outnumbered by Gaia Greenies. I had brought out my cousins to voice their needs as they own trucking companies, but they were far too few. The argument that the life of the oceans and the planting of forests was of greatest importance in buffering and absorbing any increases in CO2 was seen as outside the authority of the EPA so, they control what is in their sphere of influence.
Emissions aside, what you are doing with your truck to reach your goal of 24 mpg is laudable and important as pickups make up a large percentage of some communities. Once you have exhausted the easy engine modifications, you can peruse the aerodynamic possibilities. That opens up a world of gains as our trucks come factory equipped with horrid coefficients of drag.