I am running one. For the first 4-5 tanks, I was only getting about a 0. 5 to 0. 75 mpg improvement, but then I went to quads website and updated the module to the city tune. My mpg then shot up another 1-1. 5 mpg. So average, I have gained about 2 mpg, or about 10. 5 % (these are all hand calculated values, as the overhead is WAY off... it reads 27 - 29 mpg). Also, most of my driving (80-90%) is highway driving at 55-65 mph.