overheating still, even with a new thermostat.

What is your question?

my car started overheating. but it would get while driving in the city. driving on the highway the car would not overheat at all. then it started overheating all the time regardless of where i was. i replaced the thermostat with a new one and the old thermostat was bad. but it still overheats just not as bad as it did. now when i drive it, it overheats but only when i drive it. if i'm idling there the stays at the temp. its at or decreases slowly. any ideas?