I have never had this problem with my Grand Prix, but I did have the same issue with a 3.1L Grand Am.

If you lightly went into the throttle it would go, but if you gave it an more than about 20% throttle, it would start bucking, cutting out, etc and the more you mashed the trottle the worse it got.

Ended up being the O2 Sensor, and no codes were thrown. Might want to check that out since your O2's are pegged.

webracin