If new to diesels, remember, larger more powerful diesel engines DRIVEN THE SAME WAY AND SAME WEIGHT COACH will actually get BETTER MPG than a smaller diesel.
Said another way, the most efficient diesel is at low throttle positions, as unlike gasoline engines, which require a stoichiometric ratio, they can run on a VERY, VERY lean mixture.
Sure, if you stick your foot in it, you CAN burn more diesel with the larger engine.
We just completed a trip from S Texas to the Upper Peninsula of Michigan and back. 38' two slide 38' Alpine with ISL 400 HP: MPG average for trip 9.2 MPG. We normally take back roads (worse MPG), but normally cruise at 58 MPG (150 RPM over peak torque RPM). Yes, it WILL cruise at 75+, and likely get 7 or so MPG. Not in my budget!
And, yes, having 400 HP/1,200 LB-FT of torque is a real plus when passing, merging, or climbing a real grade.
