What should i do?

Gears will pep your car right up. By putting in a lower gear (higher numerically) your engine will be able to move the mass of the Mustang easier. You may actually pick up some milage per gallon too. That is if you can keep your foot out of the throttle.
 
Now is a good time to learn. The 5.0L is a good engine to learn to tune. By advancing ignition timing you can gain some noticible horsepower. And, it is a free upgrade. The next cheapest and noticable horsepower increase would be underdrive pulley's. You can do this yourself with a socket set on a weekend. But, like I mentioned before, get the gears. You won't want to do it yourself. But you stated that you wanted something that would rid your car of its sluggish performance and that means gears. :nice:
 
2 foot, triple stack, erector style wing. With the downforce generated your handling will improve immensely. Make sure to get 6 stickers of the company that made the wing and place them on your windshield, back glass, each side window and above the front wheel wells.