Roof, I saw a chart floating around the fuel desk of the local Pilot TS showing how speed affects MPG in a class 8 truck. (I'm sure it would roughly be the same in your DT-466 equipped trucks.) The chart showed MPG to be best between 35 and 55 MPH. It started falling off after 55 MPH with a steep plunge when it hit 75 MPH. According to the chart, every MPH over 55 MPH starts costing .1 MPG. So a supertrucker traveling at 80 MPH consumes 2.5 MPG over the 6.5 MPG he would get at 55 MPH. That's a 40% increase in the amount of fuel consumed. And no amount of fuel subsidies would cover that.
Also, I saw an article about how air carriers are cutting back on the top speed of their flights to save fuel. Overall big savings can be had by reducing fleed cruising speed by 10 MPH. See
My Way News - Airlines slow down flights to save on fuel
One of the best purchases I've made on my 7.3L Powerstroke (towards improving fuel economy) was a $159 ScanGauge that plugs into the OBDII port. Even though I have a full set of gauges, I have mine to show turbo boost, load, real time MPG and trip MPG. It will show more, but that's how I have mine set up. With it, one of the things I've learned that momentum is my friend. On the rural interstate, down a hill at 65 MPH @ 30 MPG (real time), up the other side letting it fall back to 55-60 MPH @ 20 MPG. On level ground, I've found it's sweet spot to be 57 MPH as well. This seems to be where max torque, boost, lower wind resistance come together to give me an average of 22 MPG with ULSD in a stock truck.
