There is likely nothing wrong with your car other than needing a tune up. Inspect the plugs and wires and look for excessive wear/corrosion. If these spots look bad then change the plugs, wire, and coil pack. Also inspect the radiator coolant and change that out if it's dirty or brown. Three other spots most owners over look is changing the fuel filter, rear end oil, and transmission oil. Odds are that car has not had any of those changed.
Now once all that is done don't expect the car to blow you away. Having owned almost every kind of Mustang from 95+ (V6,V8, Cobra) the V6s pre 2011 were extremely under whelming. Sure some models can "chirp second gear" but the car is still relatively slow when compared to most modern cars.