lower gear rear end?

I'm sure you can...but if you bought a v8, why worry to much about fuel? I almost bought the 4.7...but the 5.7 had so much power, and not much of a noticeable difference in fuel.

 

Did you upsize the tires? If not your set to the optimum gears already. You would loose top end and get more low end with gears. Would help mpg at lower speeds but hurt at higher speeds. Also the return on investment would most likely be longer than you would have the truck. For example I figured it out for the price of a used motorcycle I bought vs the mpg savings from the Tacoma I had at the time, the roi was around 30 years, just to break even.