I find a small engine doesn't particularly do well in large vehicles. Especially if it's power is made highish in the RPM's. That's exactly why the 5.0 is better. More RPM's mean more gas is used to get a lumpy of steel like these trucks moving. The torque in the 5.0 comes on early and gets the barge moving. Signifiacantly less RPM's with 2 more cylinders will always get better MPG's than a 6 banger that has to spin 5,500 to make 365hp and whatever torque it makes. Much more stress on a small engine, and that could actually affect it's longevity.
The reason the old 300 I6 was popular in trucks was because it has that low end punch like a V8, and yes, it got better MPG's than the V8's. Why? Because the torque to get moving was brought on significantly lower than even a 302, was almost equal in overall power output, and spun less RPM's. A lot of people want this motor, or a modernized one, back into production.
This is why V6 diesels will be important. This is why the 5.9L I6 Cummin's is popular. Low end torque gets the ship moving easily without needing to needlessly wind the engine up, saving fuel. If they were smart they'd drop everything they have and go diesel everything.
If you really think about it, it makes sense the Ecoboost gets crappy MPG's. Which is why I can't understand how Ford can sit there and claim it gets amazing MPG's. In all actuality it shouldn't, and it doesn't. But they won't ever admit that.
