2015 Ram 2500 4X4 6.4 L Hemi. I have read different articles on installing a dual exhaust system to increase fuel mileage. I am here to tell you what I did and increased my mileage by 5 mpg. The message I got from Ram forum was that I shouldn’t mess with the system. I found exhaust shop that made the exhaust system the way it should have been done but for some reason they made more money by putting one muffler then splitting into two. I had them cut off the one inch pipe from each side from back of cats and install 3 inch pipes thru 2 flowmaster mufflers and out the back.. Besides increasing fuel mileage it woke up the motor, this is a awesome motor and know by far the strongest gas motor ever.