Try rejetting to the next smaller jet size. When you re-tune tthe carb, set the idle 50 rpms on the lean side of peak.
Make sure your EGR system is working.
Get an air filter that has the proper flow rate for that engine.
Put an OEM spec thermostat in the cooling system.
Fix your vacuum leak, a whistle is telling you there is one.
If you don't know the Cat's history, get a new one.
Change the oil just before your next inspection.
Carter BBD feeding 4.2 Nuttered 6 banger = 22 MPG Hwy
If it was easy, everyone would be doing it.