Welcome to the site.
Regearing will probably show a small improvement, although probably not 10%. There are a few theads on this topic if you search around.
Other than that, I'd look into some aero mods. You seem to do a lot of highway driving and that is where the aero mods really come in handy. Plus, they're cheap.
Last thing I'll mention is to look through our
driving tips. You are already doing the simple stuff, but hopefully you'll learn something more you could be doing.