If you NEVER run the engine past 4000 you will get the most HORRIBLE carbon build-up in your secondary ports which is NOT fun to clean out later. Run it into the powerband regularly for short bursts or shift at 5K sometimes and skip gears
On the freeway, keep your speed below 80 if you can
Maintenance items of course (fresh filters, good plugs, manifold cleaning, etc)
Intake, exhaust, headers and chip will all increase mileage and performance.
