Car overheats even with a new thermostat

Hey, my problem is, that my v6 2.5l Chrysler Sebring overheats when I drive it with a thermostat. I flushed the coolant because my engine was overheating and used the chance to replace the thermostat because I that that was the reason. The car still overheated so I took the thermostat out and checked if the car overheats. Took the thermostat out, drove for quite some time and had absolutely no problems. Back at home I put both thermostats in hot water and both opened at the correct temperature.

What could be the Problem?