My 2006 diesel was getting 12.5-13 mpg towing my 24 foot enclosed trailer, quad, race supplies, and tools. My exhaust broke in front of the stock factory muffler and my mileage jumped up to 14.5-15mpg towing in hilly Pa. I bought an after marker air cleaner (didn't put it on yet) and will be upgrading the exhaust next Spring. It still has the stock computer setting and has more than enough power.