i have 2000 mustang gt with off-road x pipe, k&n air intake, 3.55 rear gears (getting 4.10s), and flows. my speadometer is off because of the gears. my check engine light is on due to the rear O2s. i bought the mills for it, but ofcorse they don't work . i was looking in to getting the tuner, it says i can fix all of this. it also says i can disable traction control for good, rather than turning it off everytime i start my car. it also says it adds 15 - 20 rear wheel horses. has anybody used this programmer??? is it hard to use?? does it really add that much horse??