I believe this TSB may be what your talkin' about.
found at:
04 TSB's
Make : PONTIAC Model : GTO Year : 2004
Manufacturer : GENERAL MOTORS CORP.
Service Bulletin Num : 050849003 Date of Bulletin: JAN 01, 2005
NHTSA Item Number: 10013486
Component: ENGINE AND ENGINE COOLING
Summary:
SPEEDOMETER ERRATIC MOVEMENT FUEL GAUGE DOES NOT GO TO FULL AFTER FILLING ENGINE COOLANT TEMPERATURE GAUGE READS HOT AND COOLANT TEMPERATURE LIGHT ILLUMINATES. *EH
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Might be, might not be.
Monica