that and check the resistor for the fans (on the fan housing) that freis out after a while. also make sure the fans work with the ac on. (easy way to see if the fans are getting power.) if they spin when you put the a/c on and dont when its off and the car is up to temp then your resistor is kaput. its around 40 bucks. get it rom ford
if rust came out when you flushed....a serious "uh oh" could be in your future. Keep an eye on your fluid levels in the degas tank/coolant fill and make sure its up to proper levels after you filled and got all of the air bubbles out.
BTW, you have to get a tune to make the fans kick on at the 180 degree (from what I understand, could be wrong though).
I have helped other people solve the same problem, most of the time they wired the fans the wrong way when they re-wired them(dont ask why they messed with the wiring, as I have no idea why), but if you did mess with the wiring make sure that the fans are actually pulling air into the engine bay and throught the radiator instead of pushing it out. [?|]
If thats not the problem you may want to go to a junkyard and get yourself a new radiator and possibly a waterpump(as i would suspect those are the two things that could be screwing you up), if you can find a part out focus in good condition.
Overheating in traffic is usually a fan problem. When the temp guage starts to creep up you should clearly hear the fans whirling.
Since you said the system was rusty, It's possible the radiator is plugged. If you can befriend someone who owns one of those inrfa-red temperature guns (even just temporarily), You can scan across the radiator. You should see the temperature decrease sort of evenly as you move across the radiator. Or if the radiator is substantially cooler than the engine, It's probably stopped up.
the fans defanatly kick in
there loud and now i was sitting in my car driving home from school on the hwy i just put the vents on cool and the fan up 1 click and the air was super cold like my ac was on