ok, that is simple then. if you have tested fuel pressure and it's good. then this condition is due to a software issue in the pcm, recalibratation of the pcm is the fix. see the following bulletin addressing your concern.
BULLETIN NO.: 03-T-02
ISSUE DATE: January, 2003
CATEGORY TYPE: Engine-02
CATEGORY: Emission Controls
CORPORATION NO.: 03-06-05-001
Engine Hesitation and/or Vehicle Lacks Power with DTC P0326 Knock Sensor System Performance Set (Install PCM Calibration)
2000 - 2002 Saturn S-Series vehicles equipped with manual transaxies (MP2/MP3) built up to and including VIN 2Z258983 or automatic transaxles (MP6/MP7) built up to and including VIN 2Z263777.
Some customers may comment about the engine lacking power when accelerating and/or engine hesitation while driving.
This condition may be caused by the PCM misinterpreting normal engine noise/vibration as spark knock resulting in unnecessary ignition timing retard.
To correct this condition continue with procedure in this bulletin