[Christ]

Aero, my friend. You've got double the frontal area, which is approx 4 times more aero load than the MB would have at speed, IIRC.

Without proper gearing for the SUV, you're not going to be loading the engine properly to get the best efficiency at speed.

I'm not saying that you've done something any less than amazing, but realistically, you most likely won't see the same mileage that the MB chassis realized.

Of course, if you brew your own BD for around $0.90 per gallon, you could realistically claim a dollar per mile equivalent to some 90 miles per gallon of normal petrol diesel.