This whole thread has made me feel a bit better about our diesel purchase. Prior to purchasing our 2016 Duramax, I was told by many that the pre-DEF models were the way to go and wondered if I should have gone that route....not that DEF is fun to deal with, but at least it doesn't appear to have had a severe impact on overall milage as my numbers reflect what many have already posted. I do often wonder what it would be if you could pull the emissions portion out as I too see the milage drop dramatically when it goes into re-gen, but I'm not the type to get into that type of thing. I do love how it pulls the TT with ease up and over the Passes. I'll just continue to enjoy the experience.