And, not having the EGR increases the likelihood of mid-throttle detonation under heavy engine load (like going up a steep grade). The USDM ECU is tuned for it...you can decrease the chance of this happening by adding additional fuel with your SFAC, but then you end up with exactly what figgie said, but worse.
They make EGR block off plates in order to get your $$$
They make EGR block off plates in order to get your $$$