We have an Ultra Power tune in our Pace Arrow. Can't give you the before and after since it was installed when we bought the rig. But I can tell you on a long grade, it's better to be moving at or above the limit when you hit a long 6% grade. If not, our Vortec 8.1 engine will be screaming and working to keep it over 35 mph. The advertised HP and Torque increase is about 60 and 50 something. But as Gary Wizard indicates, that's at very high RPMs. I don't like pushing the Pace so am uncomfortable when the tach is over 4,000. Probably OK but it makes me nervous. As far as mileage is concerned, I can't comment on the advertised .5 to 1.5 mpg gain since I don't know what the mileage was before the tune. However, the current mileage is between 6.5 and 7.5. That's pulling a Jeep with a combined weight of about 26,000 lbs. There's lot's of info on the IRV2 forum. I was thinking of doing the 5 star tune on our old 1999 Ford V10 with 275 HP. That likely would have made a difference. But the big Vortec puts out significant HP and Torque from the get go.