2005 Chevrolet Impala Over Heating

Define "overheats"
Is it boiling over and going into the red zone of the gauge or is it just running hotter than it does when going down the highway.

Turn your AC on and see if your cooling fan runs with te AC.

I'm suspecting you don't have an issue at all here. I see this issue quite often because the cooling fans on this vehicle are programmed to come on at about 226 degrees which seems to many to be too hot but believe me, it is not and it is done intentionally.

Turn the AC off and just let the car idle. Let the temp go up. Unless the gauge goes way into the red, let it go and see if the fan cycles on and back off. If the fans shuts back off it means the engine has cooled back down to the temp the computer is looking for and all is well.