How do I fix this? My speedo is showing about 5 mph faster than what I am actually doing. Was thinking of trying a computer reset.

Tires are fine, no new rims or anything like that. The only recent change is platinum spark plugs and a K&N Air filter.

Its more than likely not a computer issue. Are you sure nothing on the car has changed? as long as you stay within 5% of your original diameter on tires then you should be fine. mine shows about 1-2mph faster at 55 but i have lower profile tires, which if you have the same then that could be the issue. Just call up any mechanic shop and ask them about it and they will tell you where to take it have that checked out, otherwise i would say its not even worth the trouble. lol use it as an excuse if you get a ticket. "Actually officer, it felt like i was going too fast but i think my spedometers off. would you mind pacing me?"