It seems as if my 2008 6.4l is particular about The fuel I put in it. I only use brand named diesel but each of them causes differences in mileage and performance. My truck likes Exxon/Mobil and bp/amoco the mileage is good and the performance is up. When I fill with Shell,Chevron, or Racetrack the mileage goes down and the truck feels sluggish. I've tried many locations and the same holds true. Has anyone experience this? My friend with a 6.7 cummins can fill anywhere and his truck runs no differently why is that?