I tend to agree with otrfun that the ecoboost gets thirsty when you get into the turbos, though in my experience the cutoff for 20mpg is around 68mph. It's also sensitive to weather. The engine shines in urban driving at speeds from 30-65mph....and when towing...but not because of economy. Again in my experience, it works better than GMs cylinder deactivation in town, though it might cost you a little economy at speeds over 70mph. I put 90% of the miles on my truck driving to work and back home, so it works out better for me.
