Well this is what I see....the difference is in the motor size(the pistons, crank, and fly wheel are bigger and heavier in the 7.3).....it takes more fuel to make more power....the smaller the motor, the more fuel it takes to make a given #(hp/t) to make an object move(7-7,500lb truck)....so when you put psychics into the equation(newtons that is)....it says....a body that is put into motion(takes a certain amout of hp/t to do that) stay in motion, until forces act against it(drag, gravity, rolling resistance, weight, well you get the picture).....I am by no means a psychic major, but this is common sence....torque is what makes these things go down the road....hp keeps them going down the road....when the hp/t curve is not close together at a given rpm then it will take more fuel to achive it...like when going up a grade....the motor down shifts to a lower gear trying to get the torque up to keep it moving....if the torque curve was lower then the motor would not have to shift to a lower gear....see what I mean....I know some will.....and some wont....just my take on the matter....so if you want to get better fuel mileage there are alot of 7.3's out there for the takin.

Sorry for such a long post. Tim

 

Bought our '03 used back in May '04. Consistently get 17.5 mixed daily driving (some 2-3 mile stretches and about 20 lights) and get 21 highway (and that wsa on a bad day almost bumper to bumper). 6.0l psd, cc, lariat, 4wd, oct '03 flash.

 

I'm psychic and I predict that you are confused by physics.