There is only one way to get better fuel mileage from any 3/4 ton 4x4 truck with big tires- don't start it up. I'll never understand why so many people insist on owning these things (of all makes, not just Dodge) and then complain about fuel economy.

What were you thinking when you bought it?

If you need a truck for a daily driver, you will have significantly higher gas expenses than if you do not.

If you need better fuel economy, you will be significantly limited in what you can tow and haul.

Always, and without exception. Decide what you need for most of your use, and compromise accordingly.