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I recently purchased a 2001 Dodge Ram 2500 to put put a test engine in it. Before the engine swap I wanted to get some base line mileage from the current stock engine. From what I had read and had been told I needed to get my RPMs down in the engines torque range. I am not hauling trailers so the gearing I picked was strictly for millage. First I installing a tall narrow tire 295/70/17. My truck had the stock 4.11 gearing. I was getting 18 MPG HWY at 68 MPH at 2125 RPM. Now that I had some numbers in hand so a professional could do the math. My target was 1800 RPM at 70 MPH. Tom at Reno Driveline and Gear came up with 3.54 gears. I wanted to go with a higher gear but my axels where my limitation. My first run at 1750 RPM took me buy surprise. I got 27.24 MPG (65 MPH). I could hardly believe the results! I then dropped my RPM to 1625 and I got 27.85 MPG (61MPH). 1875 RPM got me 23.2 MPG. (71 MPH). 1775 RPM got me 23.4MPG (68MPH) still not bad. I actually could not have been happier with my results.