efeezy

Picked up a 2000GT conv 5spd few months back. From what i know ,it has a ram air type intake that sucks air from the where the passenger foglight use to be, then up to the stock air box with a k&n. It has o/r x pipe going to flows, pulleys and a 4:10 rear end. My speedo is way off from the gears and the 19 inch wheels. My question is besides ajusting the speedo for the gears and tires will i be able to get any more performace out of my car from that tuner or anything similar? Also what type of power would i be picking up with those mods? Anything else worth adding?