That is a Series II Lower Intake Manifold made for the Gen 3 blower.

Here is a pic of a non-ported Gen V Lower Intake Manifold from a Series III (with a gasket sitting next to it)


If you still have your factory Lower Intake Manifold that was on the 04 GTP when you got it, I would reccomend putting that on. It should help the motor flow a little better and hopefully reduce some of that KR.

Also, this makes me question if the motor you got is from an 05 since the Gen 3 was not used in Grand Prixs after 2003.

What color are your valve covers, Black or Tan?