In real world results I've found that most vehicles generally come with too tall of a gear in the rear end. It might make for a slightly higher number on the government highway MPG test but in real life your motor is struggling trying to move, so you have to use more pedal all the time. By going to a shorter gear (higher numerically) your vehicle can accelerate easier with less pedal. If you drive 50K highway miles per year on cruise control then you pay prefer the taller gears, but the rest of us get as good or better mileage with shorter gears. My Bullitt comes with 3.73's and I still have enough gear to run 60 at 2000rpm so the motor isn't working very hard or burning a lot of fuel at cruising speeds. With the taller gears I'm sure that 5th gear is pretty much worthless to you.