I just completed a trip this last weekend. I filled up until it was running out of the filler neck, reset the trip odometer to 0, and reset the overhead console fuel/mpg reading. I got directly on the interstate and set the cruise control on 75 mph. I stopped twice at rest areas for bio breaks (shut the truck off for 10-15 minutes each time). When I arrived at my destination I pulled into the fuel station with exactly 805.1 miles showing on the trip odometer. I filled the tank very slowly to minimize foaming and I filled it until it would run out of the filler neck. It took 45.7 gallons, which works out by hand to 17.6 MPG. The overhead console was showing 18.1. I was pretty happy with that. The truck is completely stock other than having a 65 gallon fuel tank and a tonneau cover. I just passed 6,000 miles on the odometer.

Over the past few weeks I've also seen my combined city/hwy driving improve to about 16.1 MPG. I have no idea why the mileage is improving other than the weather is cooling down, so I drive now with the AC turned off. Maybe the winter fuel mix burns better too?

The majority of this trip was in very flat terrain (Eastern Colorado & Kansas), where you are running 0-2 psi boost at 75 mph on the highway. I did notice that most of the time, the EGT was in the 850 to 925 degree range. However, about every 3-4 hours the EGT would shoot up to 1125 to 1200 degree range and stay there for about 15-20 minutes, doing a regen I assume. During that time, you could watch the MPG on the overhead steadily decrease from 18 or so down to about 16.3. As soon as the EGT dropped back into the 850 range (and it would do this quickly) you could watch the MPG steadily increase until it got back up to the 18 range after about 15-20 minutes.

So, I have hope. If Quad gets a mileage module built for the 6.7 that will give another 1 to 2 mpg under these conditions, I would be getting right at 20 MPG. I could live with that, especially considering the power this truck has when pulling loads.

 

Have you tried it at 65 mph? Even my 05 hemi has gotten almost 20 on a tank at 65 or even a tad under, 64. We're pushing a lot of air.

 

It does get slightly better MPG at slower speeds, but there is no way I can drive that slow on the interstate for an extended period of time.