To help illustrate wilber's point, I made a comparison on another forum showing the difference in HP generation between Diesel and Gas motors. As you can see, both 6.7's produce far more horsepower at far lower RPM's while the gas motors take a while before they hit their horsepower band. So say you need 200 HP to pull a trailer, the Diesels have that power available at 1500rpm up to their respective redlines. The ecoboost makes that power at 2500rpm while the 6.2L ford takes all the way until 3100 rpm before it's making that power. This is all assuming a 1:1 engine to drive ratio. Gearing makes up for these deficiencies though but it just shows shy Diesels have so much more oooomph!
Trying to stick a google sheet in here:
If that doesn't work, here's a link to a PDF of it:
HP Spreadsheet