So i purchased my ram late December 2016, when I was driving from Kentucky to Michigan I was getting about 23.5 - 24 average mpg at about 78 miles per hour. Now doing the same drive I am getting about 18 mpg. How ever I have changed two things tires and air filter. I am running factory size tires they are cooper atp' s. My air filter is a drop in k&n. I cant imaging that the tires would decrease fuel economy by 5-6mpg nor the air filter. Does anyone have this issue? Truck has about 30k miles on it. I use mobile 1 5w-20.