Any No. for those 4th Gen. Cummins. I would like to get one but I am afraid that they can't hold a candle to my old 96 12valve.

 

I get about 17 city and 21+ highway. Bone stock other than a K&N Filter in original box.
I towed my 29' toy hauler (without toys) to Yellowstone twice now. Averaged 10MPG both times. (First time at $4.80 gallon!)
I only have 34K on the motor and can't wait for the engine to "Break in".
My neighbor has the 6.7 with 35s and he gets around 12-14.

 

When I travel to Washington State from LA California at 5 mph over the speed limit I get about 22 miles per gallon. When towing my race car i travel at about 58 MPH and I get 18.5 to 19 MPG depending on traffic. I do have a banks 6 gun system with a top loader.
I have found that if I take my time and drive with the tack at 1600 RPM my truck will get 26 MPH all day but it may take two days before I get to stop to go to the bathroom with the need to stop for fuel.