Very true Shiner.
The thing is, the big 3 now days use pretty much the same strategy. Same common rail, pretty much the same turbos, pretty much the same injectors, pretty much the same injection pressures..........everything is pretty much the same except for the name on the valve cover.
That's why they pretty much get the same power/ gallon burned out of each engine.
My buddy is putting out 525 HP to the rear wheels in his 2003 Cummins. He has compounded twins on it with an intake and a few other goodies. He gets 23 MPG average on the hwy solo.
He has never tested it but I know that thing is REALLY dirty smog wise. I can guarantee you that thing is making a ton of NOX. It has to be because it is so efficient in combustion burn.
Unfortunately, or fortunately depending on which side of the fence you're on, the manufactures can't play the game he is playing.