Just got my TB w/ 6.2L and no DFM. Drove 92 miles each way across state, mainly flat with light up/down hill gradient. Averaged 22.7MPG at 60MPH.
EDIT: After digging, I DO have DFM. Crazy, I can't tell when it's in use.
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Should improve with K&N filter/elbow kit and tonneau cover. Going to try for 23MPG or better. My 2016 Canyon All Terrain best MPG was got 27.2 on the 3.6L w/ 6 speed trans. So I'm actually pretty surprised on a Full Size, Half Ton truck that's gotn4x4 capabilities to be getting anything over 20MPG with a large displacement engine.