If you didn't regear it that's why your fuel economy is suffering. say you had 31 inch tires originally then you went to a 35 that's the same as Towing approximately 4000 pounds all the time. The only way to compensate that is to get your truck re geared. the reason why my fuel mileage increased so much with a smaller tires is because my truck can't even engage 5th gear until 75 miles an hour with the 35s. And with aerodynamics like a brick it's working the engine much harder. yes lighter tires will improve your fuel efficiency however you've already destroyed the aerodynamics of the vehicle by not only leveling it, but also lifting the front in 6 inches higher which means now there is 6in more air underneath to get turbulent which means more drag. what can I say you got to pay to play this is just part of owning a lifted truck. as the truck ages those heavy wheels and tires without a re gear are going to wear the engine and transmission out "sooner." (nobody knows longevity we could be talking the difference between 1 million miles and "only" getting 500k miles) Sent from my SM-N975U using Tapatalk