My uncle has their power programmer thing in his GMC Avalanche (the pickup/SUV looking thing). Granted, this has nothing to do with a Mustang application, but the unit was excellent and it made a substantial difference to the truck. Best part of the setup is it can easily recalibrate the speedo for diferent gears, taller/shorter tires, adjust performance based on whatever gas you wish to use, etc...and it can be set back to stock in a matter of minutes. I think they make the power programmer thing for the Mustang...not entirely sure though.