MADDOG is on one end of the scale, I'm probably on the other. I have a 2012 2500 6.7 CTD, crew cab w/ 8' bed, that is emissions stock, suspension stock, and tires stock. I do a roughly 1 hour commute each way to work every day, all interstate traffic through downtown Tampa. I have a heavy right foot and am usually doing in the vicinity of 80 mph. I have a solid 15 mpg over the past 4 months in an empty truck, as indicated on both the EVIC and from hand calculating my mileage vs fuel from the pump. Pulling a -loaded- (probably closer to OVERloaded) 16x7 dual-axle utility trailer I drop down to between 13 and 14 mpg.
I am considering a full delete but haven't pulled the trigger on it yet. I see a lot of positives but also read about more than a few negatives.
In the very near future I will be adding a suspension lift & level and 35's... That will definitely effect my mileage, I may look into a mild tune to offset the loss. Or just live with it, will see when I get the work done. I don't drive a truck for mileage, I drive one because I need one (and because I want to.
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