Moon... Might... I have lots of photos of special stuff that would work for a fuel economy article...

2- Scenario #2- You run at 75-mph on the Interstate most of the time in your pickup/Suburban without a load.

Wind drag increases exponentially, with drag becoming an ever more increasing factor above 65-mph. At 75, you need a turbo. The efficiency loss of pumping exhaust through a turbine is now overcome by the increase in power and efficiency offered by a turbo when operating at the higher power requirements of 75-mph.

Still, a 6.2/6.5 built as the above N/A 6.2/6.5 would apply, but we simply add a turbo and a single 3" mandrel bent free-flowing exhaust system. Gear the vehicle for 2000-rpm at 75-mph, and shoot for somewhere in the vicinity of 3-5 psi boost pressure at 75-mph on a level highway.

As mentioned above, wind drag is significant at 75-mph. Anything you can do to decrease drag will pay big dividends in fuel economy. Under-bumper air dams reduce drag, as does lower vehicle ride height. Lose the exterior accessories (like bug deflectors, etc.) and run narrow radial highway tires with maximum air pressure.

Differentials..... Open diffs have lower drag than limited slips.

MP