The car overheats when driving with A/C on. It will go back to normal tempif idling with A/C on. Fans both work under hood and thermostat was just replaced. Upper hose has water flowing thru it once engine's warm. Recently put new coolant in (problem was happening prior to change) and bled the system properly. I'm stumped so anyhelp diagnosing this would be much appreciated. Thanks!

 

I'm thinking:

1) thermostat - I know that you changed it, but that doesn't mean it's not bad. Take it out for a while.
2) water pump - Flow at idle with the cap off doesn't mean that it is providing adequate flow under load.
3) water temp sensor - sensors can do weird things when they die .... even weirder when they die slowly.

Take a look in the DIY section for diagnosing overheating .... there are probably a few more things to look at in there as well as diagnostic measures that will help you find the problem .... good luck!