OK - I'm not selling anything EXCEPT one thing that we all know......Here's the facts - and if I didn't experience it I'd say BS.......but I did almost duplicate it.......
I just got back from a 700 mile concert trip (Martina Mcbride) and here's what I discovered regarding mileage....see how my truck is equipped....
1. I was travelling south from Vancouver Washington to Medford Oregon - I decided to run the 1st part for mileage - as I had hours to kill.....
2. The freeway is essentially flat - the temp's were in the low 70's - No Rain - or wind -
3. I decide to go no more than 56 MPH - that's right 56 MPH! I only passed two vehicles and was passed by everybody else. However with 3 lanes and relatively low traffic -
4. I went 161 miles and noticed that the fuel gauge was obviously much higher than normal - I filled up - I mean I filled up you know the fuel is 1/2 inch from the top - just as it was when I left - 5.85 gallons -

You Do The Math! HONEST NO BS.
5. Having almost needing CPR - I decided to push the speed a bit and see if it changed the result...... So for 147 miles I didn't exceed 60 and was always around 58-59 - result --- 147 miles - and 5.95 gallons...

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6. After the concert I drove usual as I needed to get home before dawn - and at mu usual 72 MPH I was back in the usual just under 20 MPG.
OK - I want somebody else to try this experiment and see what they experience..........