Yabutt, what did your NPR cabover get ?
Never owned an NPR..... the cabover was a 1996 diesel Hino (commercial Toyota related). Got 13 mpg empty at interstate speeds and 10 mpg fully loaded. And that's with speed limited to 65 mph empty (no governor, that's just all it would do). Box was much heavier than a typical Isuzu NPR however with heavy plywood walls, E track everywhere and AHT 8 x 7 foot lift gate (that also served at the rear box door)
The current 2011 Chevy Equinox is gas, with an all composite box that supposedly only weights 850 lbs...but it also has AHT lift gate, and more... integral hydraulic stabilizing legs, and integral scissor lift to lift the entire box to dock height if necessary....so a bit of weight added there. The box is labeled "Eco" because it it so light I suppose the the theory is it would save fuel, but the reality is a joke...even with one of those "bubble" attachments at the front of the box it gets 9 mpg interstate speeds empty !
Penske box trucks of similar ilk (except with no lift gate or legs, etc) I have rented and got 10 mpg. Having said all that, the Chevy is waaaaaaay more pleasant to drive than the Hino. The HIno was so LOUD and so SLOW that I would be very reluctant to actually use the thing unless desperate. But the Chevy is quiet, smooth and FAST.....such that I had no qualms about making a 400 mile trip (each way) recently to pick up a Hardinge HLV-H (in the mountains !) So nice to be able to go as fast as everyone else on the super slab and actually hear the radio or a CD.... I haven't put it to the test for fear of speeding ticket but it feels like enough gas pedal left at 75mph to go 100 mph if I wanted to on the flat.
But the MPG is a bummer...considering the composite box, I expected at least 11 mpg.... 9 mpg is ridiculous indeed. Thank goodness gas got cheaper about the time I bought it and stayed that way so far....down to $1.85 around here in some places now.
My 2007 Dodge diesel dually crew cab got 19 to 21 mpg at interstate speeds empty as I recall. Mileage went down to about 16 hauling empty 28 foot gooseneck trailer (open flat bed, 8 wheels) and down from there the more weight added to it. This is all manual calculations btw, as one can't really trust the vehicle mpg computers.