Yeah I do. Right now my truck has the 4.2l v6 and gets around 16-17 city. Now I notice you say "big heavy trucks", well the 4.2l only has around 205-210 hp. This hinders its fuel economy. The ecoboost will be putting out around 400hp, so lack of hp will no longer be an issue, yet you will still be driving a v6. In my opinion the ecoboost will definitely top the 4.2l and all the current engines in mpg.