All the dyno shops on LI are gonna wanna suck you into a chip. Your best bet is buying a datalogging wideband kit and tuning yourself on the street. YOu will get a better tune on the street because its a REAL load on the car unlike a weak 4th gear dyno pull. Stay AWAY from mustang magic
Try
www.stangtuning.com for PMS help. I have a PMS and the basics are easy to use.