I got an 04 Sierra with 62,xxx miles I bought from original owner who kept it well maintained.
2 days ago after about 2 minutes of driving it the temp was about 250'. I turned it off and the needle stayed there and didn't go down.
I replaced the thermostat and turned it on and the needle went down to about 212' and wont go down after I turn it off.
Shouldn't the needle start at 160' when you first turn it on?
Is there something else wrong?
The other needles go down but not the temp one.

 

Does it sweep when you turn key on, or is it just stuck there? Have you tried disconnecting the coolant temp sensor? Not uncommon for the stepper motor in the guage to go out, usually its the oil pressure than goes first though...

 

Its stuck there, it doesn't move. It just went down a little after i changed the thermostat.
Where is the coolant temp sensor?

 

If its not moving i doubt its the sensor, but it is in the driver side head in front of the exhaust manifold...

 

Stepper motor is bad in the cluster im sure. I can rebuild the cluster for you. 100 plus return shipping, or if you local to Fairfield CA you can swing by my work. Only takes about 45 min to finish.

 

I'll see if i can get it repaired locally, if not I'll send you message mike.