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.
13 Mustang GT CS - 380 RWHP 370 TQ
13 Mustang V6 PP - 270 RWHP 260 TQ
95 Mustang SVO - 400 RWHP 400 TQ sold
08 Mustang GT - 285 RWHP 305 TQ sold
99 Mustang Cobra - 280 RWHP 290 TQ sold
11 Mustang V6 - 270 RWHP 260 TQ sold
97 Mustang GT - 190 RWHP 250 TQ sold
00 Mustang V6 - 145 RWHP 184 TQ sold
98 Mustang V6 - 125 RWHP 210 TQ sold