Looking for some experience or opinions for gearing options. The truck is a 99 350 with the zf6 trans 4x4. Originally the truck had a 10" lift with 40s and 4.56 gears. Since then I have dropped to and 8" lift and currently running with a 38 tire. With the 40s Highway speeds weren't bad maybe turning 2000rpms at 70mph. With the the 38s at 70mph its almost 2300. Fuel mileage sucks, I drove across state and hand calculated 20mpg with the 40s, and over all acceleration isn't what it used to be either. So the 4.56 are to tall of a gear for the 38s. Couple of choices, regear the axles, or go with a gear vendor overdrive unit. I hAve no experience with the gear vender unit and do t really have many videos on YouTube of real truck reviews. Not sure what to defeat to either. I know there are charts and what not but would like to get some input on these options. What do y'all think???