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 Driv