application?

by don
(new windsor, ny USA)

1998 vw jetta 2.0L 5speed; what system do you suggest? I drive 85 miles 1 way-partial local majority highway, speeds 60-75mph currently i am getting 30-34mpg monitored over a 1year time period fueling every other day and calculating after fillup. I am very experienced with automotive wiring and previously owned my own repair shop. Being somewhat skeptical I do not want a high initial cost, building my own system is an option. Your suggestions please. Thankyou