I have driven my 4.56's around for about a week now and my gas mileage has climbed from 9 to 14mpg. Combo of city and highway driving. My power is now back also!! However my speedometer is way ahead, it says 80 mph when I'm goin 70mph. If I could have done it over again I would have saved up for lift, tires, and gears at the same time. The power loss and horrible gas mileage was 6 months of hell! Its definitely better to get all 3 at the same time. As far as tach, my engine is only taching about 900 rpm higher at 65mph than it was before so the 4.56's fit perfectly with the 36" swampers.