Fuel mileage

With light loads im averaging 8.6 mpg in my Volvo.I used about $100 less fuel last week than "club foot".Personally never wanted to try to log 800 miles a day.Thats kinda questionable . JMO

 

My kw is running a 550 kitten with a 18 speed non neutered and I get around 5.3-6, I had a loaner freight shaker with a 500 cat for a couple of weeks that was set for 64 wide open and it got 6-7 in the desert and 4.7 -5 ish in the mountains almost the same engine but completely different mileage, I will keep my non neutered long legged mountain cat and get a constant 5-6

 

Since I was born and raised in Western Europe, fuel economy is in my DNA. So I'm completely anal about aerodynamics, rolling resistance, and speed.

That said, I took the governor of the truck, and now run a 9 foot gap between the truck and van to make the bridge formula work on 89,000 lbs. We need the speed to make a reload appointment on one run, and to stay under 13 hrs drive time on our Calgary run. Add to that the PNW mountains, and we're in the low 5's on winter fuel. Makes my skin crawl thinking about it, but it's far more profitable than adding a day to each route, and it keeps the driver from bolting to another gig.

 

There is a truck in our fleet that if I baby it I can get 5.7 mpg. If I treat it rough I get 5.2. Now both of those mpg's are running at 65 mph. Not that much of a difference for me to be worried about.

Tell you the truth I don't care what the truck gets unless it puts me in a spot where I'm on fumes and can't get fuel which thanks to prior planning hasn't happened to me yet. Had a co-worker coast into a truck stop out of fuel. His truck died on the off ramp of the interstate.

 

I get 7.4 I am piss it is not over 8. I don't think it will be over no matter how I drive because of all PA mountain do and heavy loaads

 

So my T680 is specd at 485 with 3.25 gears. My question is what is a realistic expectation for mileage?