NEVER_NEVER take a thermostat out of a modern engine. It will not allow the computer components to work properly. That engine is designed to operate at 200 degrees F. It will also cause the water to flow through the engine too fast not allowing it to cool the engine. It waill also ruin you heater core with full water pump flow.
Now that we are over that, have the radiator checked, I supect your radiator is not flowing right. It is a common GM failure especially if the coolant hasn't been changed as required.
It on the off chance could be a defective sending unit. Put your T-stat back in and change the sending unit, it is right by the T-stat housing and has one wire. Inexpensive repair. If it continues have the rad fixed. Good luck
Friday, April 14th, 2006 AT 12:04 PM