Have you tried the idle re-learn?
Disconnect NEG from battery for 30min
Reconnect and start car, let idle as eng gets to operating temp. Let it idle a little over a minute
Turn on A/C to MAX, let idle little over a minute, turn off A/C
Then drive the car for at least 10 miles
Made a huge difference for me, even though I have a 04 Mach1. I hear this is more commonly needed on the new 5.0's.