Temperature gauge reading hot while engine isn't on 2000 Cadillac Seville STS

I had this car since November of 2013 no issues, but now the temperature gauge is saying my car is running hot, so I naturally replaced thermostat, water pump, did a coolant and radiator flush, the engine isn't running as hot as the gauge says, but it keeps shutting my car off as the system says it's overheated. Help?

Asked by for the 2000 Cadillac Seville STS
Have the engine coolant sensor tested, and the temp sender as well.
Thanks will let you know how it works, how do I locate these?