6.7 mpg on DD15

Why decrease psi to increase less resistance? Correct psi is what increases rolling. Maybe the engine has a deficiency somewhere. Wouldn't a dyno test give him some in-depth info?

 

I drive a 2010. That's about what I average pulling pretty light loads.

No APU, so I idle about 30 hours a week.

Edit: On a side note, I really like the truck. Big truck and nice sleeper. Have absolutely no sensor issues, thanks to a good shop. Regens when I want it to. I only regen about once every two months.

 

When was the last overhead done on the engine? If they are out of adjustment you'll have mpg and power issues. When was the fuel filter changed last? I have found changing mine every 25k miles helps keep my mpg up even though the book says change it with the pm every 50k miles.

What kind of fuel do you use? Loves? Pilot/flying J's? TA/Petro? Loves has the worst fuel quality over all. Pilot/flying J's have high moisture and biomass content and it's hit or miss on the quality control. Overall the ta/petro have the best quality for a big chain fuel place. Mom and pop shops usually will have the best fuel overall. For every 5% of biomass in the fuel you'll lose 0.2 mpg.

Try driving like a prime truck, keep the rpm's at or below 1300. Shift between 1200 and 1300 and keep the boost down below 20.

As Kevin Rutherford says, you need to focus on driving for mpg, it doesn't just happen because you have cruise set. Get his scan gauge to help you monitor what's going on while you drive.

What kind of tires do you have on the truck? Do you hasn't super singles? Does the truck have the aerodynamic skirts on it? Do you have wheel covers on your drives? What about your trailer? What tires? Skirts? Tails?

All of those can help improve your mpg dramatically. As you can see from this list, there are many factors to getting good mpg. I have a 2015 evolution with 118k and my 90 day average is 8.5mpg but I drive like a prime truck usually doing 62-64 mph.

 

The easiest thing to do right now is slow the truck down for a week and see if your mpg increases, then from there start making adjustments so you can track what works and what doesn't. Keep really good records on before and after whatever change you do and don't do more then one change at a time. Make a change run with it for a few weeks to see if it helps and then make another change until you get your average above 7.5mpg.

Slowing down is the easiest. Then I would look at wheel covers. I got the deflektor wheel covers at Christmas and saw an increase in mpg by 0.2 mpg pulling the same load multiple times that week versus the week prior without them. The wheel covers would run you about $200-300 for your drives.

 

2015 cascadia I was driving the mpg was 5.9 to 6.5 max. Driving 70 mph