[thstone]

The ECU has the ability to "tune" itself as you drive. It will slowly adjust several engine parameters like fuel mix, timing, and how they vary over temperature to provide the best performance and lowest emissions.

These adaptation parameters are stored in the ECU and lost when the battery is disconnected. As Overdrive and Topless have suggested, just give the engine about 100 miles to refine the engine tuning. Spirited driving will help the engine to tune itself more for power than low RPM emissions.

If you're still having an issue after that, post back here and someone will suggest the next logical step.