No, not at all Shiner.
It's that, PLUS many other things like total weight of the truck, surface area of the front end and even things like height of the truck. It's very difficult to compare one truck to another.
Here is a good example. Ford changed the front air dam on the front of their F250 and picked up between 1/4 and 1/2 MPG JUST with changing the chin spoiler. That's a BUNCH! Just with a chin spoiler change on the front of the same truck.
HP is just a measurement of lifting weight in a set amount of time. That's why city mileage suffers so much. You're lifting that weight over and over and over for every stop sign or light you hit.
In any event, I started this thread to try to explain why adding power to the SAME exact diesel engine will not hurt your fuel mileage unless you use that power. This is the exact reason why tuners on diesels don't cost mileage. They add power by adding fuel and timing. If you don't use that power, there is no mileage penalty.
