I can't think of worse years for bad fuel consumption on Dodge trucks.
Depending whether the vehicle in question has Federal or California emissions package, there may be a black contraption mounted on the side of the air cleaner housing. This is called the OSAC valve (Orifice Spark Advance Control). This valve interrupts vacuum to the Vacuum Advance Diaphragm on the distributor when the engine reaches temperature, slowing down timing advance under throttle.
You can eliminate the OSAC which will improve drivability (and by default reduce fuel consumption) by connecting the vacuum port hose on the carburetor directly to the vacuum advance thereby providing full time vacuum advance action. However, with the engine set at the correct timing this usually provokes pinging at lower RPM. This can be eliminated by replacing the primary spring in the distributor (primary spring has two small loops one at each end) with a heavier one.
Better than that is to recurve the distributor to allow a 10 degree advance basic, to about 34 degrees total if you want to run 87 octane. I would not advise modifying the Cold Air Inlet Door (trap door on the air cleaner housing) if increased gas mileage is your goal.
Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 129109 miles.
