2004 Dodge Ram 2500 Hemi. What modifications will improve fuel efficiency?

Best way is to modify the way you drive, Look on the net for the best driving habits to increase fuel economy. Right foot to heavy. Stay away from the gimmicks that say this item will give you better gas mileage. They make money mining the miner for example every gold miner needs a better set up to find gold and a seller with all the new tools is always there with a high price shovel. Make sure air filter and service is up to date. Keep tire pressure at the tires recommended pressure on side wall. Leave earlier or later to avoid high traffic areas. Other items that can help like better exhaust will cost a fair amount of money and time to offset the initial cost of it. Get the mid grade fuel. No need for top grade it does not help enough to offset is price but lowest grade burns up faster with less power.