Can anyone recommend a performance module for 3800 SII that actuall works for better
 

Can anyone recommend a performance module for 3800 SII that actuall works for better fuel economy? If so what increse did you see?

Do you mean a chip? Don't waste your money.

You have two options, you can buy a PCM with a canned tune that could be modified to change whatever aspects you are looking to change, or you can take it to someone who knows what they are doing and has a tuner to get a custom tune for your car.

The custom tune is going to be yield better results.

As Roy mentioned, don't waste your money on chips or other scams that just manipulate your sensors and cause more harm then good.