My company has 10 DD15 equipped test trucks.  I had my doubts, but I'm sold.  They're averaging 7.1-7.2 mpg at 70mph Averaging 7.9-8.0mpg per tank. With lower than anticipated maintanence costs. It ain't cheap, but damn it'll pay for itself fast.

Need more info.

How are the trucks set up, as far as gearing and tire size and trailer design?
What horse are they spec'd?

Quoted: Need more info. How are the trucks set up, as far as gearing and tire size and trailer design? What horse are they spec'd?

I don't know gearing, but we're running 1350rpm at 62mph (where i cruise for optimum mileage with my detroit 60)  The test trucks all have Eaton Roadranger Autoshifts. They're a split 5 ten speed. Freightliner cascadia mid roofs with flatbed trailers, so we have loads of all shapes and sizes on em.  They're gonna be standard power, I'll look it up shortly.  My 60 is 515/2250 and I'd imagine that the dd15 is about the same. Not sure about tire size, but they're Michelen X1s so we save 400 lbs just in tires on the tractor.

I average 6.5 mpg with a dd60, eaton road ranger manual (ten speed), Cascadia midroof, with 563,000 miles.  I could get better, but I also like actually getting miles.

Tire size and gearing (I hope, to follow later)

How do you pick tires?  My company runs trucks that spend a lot of time off road, so we don't use the newest low rolling resistance tires or super singles.

What are ya'll running?

Quoted: How do you pick tires?  My company runs trucks that spend a lot of time off road, so we don't use the newest low rolling resistance tires or super singles. What are ya'll running?

Super singles, we spend a good bit of time on muddy, rutted up, nasty, jobsites too, they perform great.  Better traction in the mud for sure. I was skeptical but I'm impressed.  Main problem with em is if you blow one, you sit. You don't ease into a shop, you don't get to an exit, you put it on the shoulder and you sit.