2004 H2 Engine Temp Gauge goes Nuts

[Olfart]

2004 H2 49,000 miles
Temp gauge normally reads OK...abt 200 degrees. But recently once in a while it slowly climbs until it reaches max temp and when I cut off the engine it reads about half scale instead of going back all the way to the left. It continues this for a day or so and then finally returns to the correct reading. The engine is not overheating. The only thing done to it which might be related is the replacement of the water pump about 3 months ago.
Purchased the Hummer used with 39,000 miles about 3 years ago and love it although I have had alot of work done to it....thank God I purchased a 3yr extended warranty...althought that has now expired.
Tnx for any suggestions on the temp gauge problem

[Easy Ed]

Might get it checked for any code for starters, most part stores can help ya there.

[HumminNBoatin']

Definitely could be as simply as a bad thermostat. Literally a $10 Part. change it out and see what happens. If problem still persists might try an engine temp sensor. thats pretty cheap too.

[Olfart]

I checked codes and there are no problems shown. As far as as the thermostat goes... the engine is not overheating the gauge just reads too high a temp. And after the H2 sits overnight and is definitely cooled down the temp gauge will read about 200 degrees when ign is switched on. It will continue to climb slowly to the far right as the engine heats up. Then the next morning it will read properly until it decides to screw up again which could be a couple of days or weeks. So I'm suspecting a bad sensor or a bad gauge, but am looking for any other suggestions before I take it into the dealer because warrany expired in Sept and so the $$$ will be on me

[Easy Ed]

Circuit description (2003 Service Manual)
The powertrain control module uses the engine coolant temperture to monitor the engine for an over temperture condition. This condition occurs when the coolant temperture is above 132 degrees C (270 degrees F). When an over temperture condition is present, DTC P1258 will set. Blah, Blah, Blah

With it not having a code I would say it would be the gauge.

Another thought, wasn't there some problems with insturment panel clusters and the gauges acting up mentioned on here before ?

This one is about the speedo. http://www.elcovaforums.com/forums/s...strument+panel
Same here speedo http://www.elcovaforums.com/forums/s...strument+panel
Complete cluster not working http://www.elcovaforums.com/forums/s...strument+panel

Not found any on the temp gauge though ?

[Olfart]

It now looks like it's the gauge that's bad since it reads all over the place and the engine isn't running hot. Even with the engine cool....sit overnite...it reads about 200 degrees. Since this will most likely involve replacing the whole instrument cluster I think I'll just ignore it until some other gauge in the cluster goes wacky.
I rescanned again today with the engine both cold and hot and there are no codes coming up bad.
If I do happen to get an overheat condition it will throw up a code and I will get a warning on the DIC. Since I don't overload the engine....h'way driving only...and a few dirt roads to my house...I think I'll be safe doing it this way.
Any comments for or against would be appreciated