I've put 16K miles on mine, 85% of those miles towing +10k lb 5th wheel camper and my lifetime fuel mileage is 10.5mpg (hand calculated). It gets somewhat better on highway empty but I don't know how much better because I rarely drive empty, though I estimate 14-15mpg. Senix says it best, these trucks were designed and built to tow, if you're just going to commute in it and you have concerns over fuel economy, may want to skip this one. If however you tow, well I recommend the 6.4. I'm in the relative minority here on the FTE as I'm not a fan of deleting and tuning - however I'm not deleted or tuned so what can I say about either.