Well comparing the 91 Tune to the Stock Tune I lost about 2 mpg avg, BUT it was a hell of a lot more fun and powerful/aggressive. The power felt like it was there there when I wanted it unlike the stock tune. This was taken from the computer, which I trust to be within a 0.25 mpg from previous hand calcs. I ran mostly 70mph, hit 90 mph once or twice, AC blowing, with a rolling terrain. It was the PA Turnpike. Not to bad IMO, I still avg 18-19 mpg. I may try a different Tune for the drive back and see what it does. Ill keep ya guys posted.