2001 Dodge Durango still running hot after thermostat been replace what else would it be?

Bad radiator cap, blockage, new stat is bad, bad coolant temp sensor, fans not working, air pocket in system, worn blades on waterpump, inadequete mixture of coolant and water. Two other things to check....There is a temperature sensor next to the thermostat. They cost about 12 bucks, a standard item, and they are known to degrade in performance over time. Mind you, everything on a fuel injected engine is controlled by a computer module and sensors, the computer adjusting parameters according to readings it gets from the sensors. A bad cooling sensor would not tell the computer to send current to the cooling fan on the radiator. The second thing to check is your radiator itself. Corrosion will build up on the aluminum vents inside, and prevent flow of coolant, and even though your water pump is pumping, the flow is restricted (depending on the antifreeze mix you use), and the solution to that is to have it flushed out. They sell bottles of stuff that you add to your radiator to clean it, or you have it professionally done. To have your radiator flushed insures it is clean, and insures you have the PROPER mix of antifreeze. Too often, shops use the 50/50 mix of antifreeze, and common knowledge dictates that bigger 8 cylinder engines need a richer mixture, like 70/30, especially during the summer. Hot water has way much more pressure than hot antifreeze, and the friction of the mostly water mix could be relative to the "running hot" condition. so, 1st.....Run a richer mix of antifreeze, drive it and see the temperature change. 2nd.....Have the temperature sensor changed. 3rd.....Flush and clean the radiator. Betcha nothing your mixture of antifreeze is too thin to handle this hot weather. Hope it helps. Peace.