also in terms of the engine, there's intake, echaust, all their components so, cold air intke, heads (or port and polish your current ones), valves, headers, nigh flow cat (or no cat but i think the environment's screwed up enough as it is), cat back system, port and polish exhaust side of heads. all this will get you beter fuel efficiency if you don't floor it and drive with gas mileage in mind, in other words, accelerate slow, shift early, don't speed. shifting early is just a rule of thumb, there's a specific spot where you'll get the best efficiency but you need some graphs of some sort from the manufacturer, then you need to understand them, but for a rule of thumb, the lower your rpms the better your mileage.