"I run light loads, pulling mostly boats and new trailers. My truck is an Ex-Roadway truck with a single axle rear, and a M-11 Cummins set at 400 HP. I was already getting 8.3 mpg, and I told Mr. Dees that I didn't think it could get any better. He told me that if it didn't I had 90 days to get my money back with his satisfaction guarantee. I've run the unit for a few weeks now and am getting 9.9 mpg. Doing the math, it is just over a 20% gain in economy. Yes, I am telling all my friends"