Only get a PCIII if you are getting a FUll System upgrade exhaust. Or anything to do with the exhaust for that matter; Cutting the cat./slip on/Headers ect. PCIII just controls air/fuel mixtures. If your not changing your exhaust, your ECU is best an should be left alone.
If you are getting a new exhaust ...it will help... but only if u know what ur doing. Get it PROFESSIONALLY Dyno'd for full potential.