Q: 2005 hummer temp gauge drops off and than sputters and sometimes dies. temp up and drives fine

It has to first be determined if the actual engine temperature is really fluctuating or instead the stalling is just simply a coincidence with a gauge malfunction. A scan tool can measure engine operating temperature. Fuel supply faults are a possible cause of stalling as are vacuum leaks and faults with engine sensors. On many Hummer models, it has been reported that faults with the throttle body commonly cause stalling and consequently that might be a good place to start the diagnostic. YourMechanic offers a stalling diagnostic. If you request that service, a certified Mechanic, dispatched by YourMechanic right to your location, will get this problem resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.