2005 Chevy Impala overheating

Have you checked it for leaks?
Make sure your thermostat opens at normal operating temp (when engine at normal operating temp/starts overheating, is the upper hose hot? If not replace your thermostat).

Other possible problems include:
-clogged radiator (if you have an infrared thermometer, you can check for clogged spots inside your radiator)
-weak water pump
-internal engine leak
-cooling fans don't come on (when car starts overheating, do the fans come on?)
-loose serpentine belt (is your belt tensioner OK)
-bad hose

Also, if you have a scanner that reads sensors inputs and a thermometer, compare the temp your sensor reads and the actual temp you get with the thermometer at the thermostat housing; if about the same your sensor is okay. If they are not the same, your coolant sensor is no good.