Hello Diane!
I'd love to have a look at it, but won't be near Orlando for awhile... probably mid to late winter. But if you come north, follow the east coast until you hit Hampton Beach (NH) then turn left and go inland for about an hour... : )
OK, kidding aside... I just figured out my new computer wasn't downloading all the posts. Hopefully, I've backtracked and not missed anything... well, unless posted it is fixed... that would be great.
Sounds to me that you are describing that you are overheating only when the radiator fan should be coming on. This would be a problem only when running and stuck in stopped or slow traffic, (or sitting idling when working on stereo system). And since you say the fan does run with A/C on, that would narrow it down to temp sensor, related relays/controls, wiring,... OK not that narrowed... but I would be finding the temp sensor (most likely in the radiator but not sure at this point) and unplugging it and jumpering it to see if the fan then runs. If so, bad sensor. This assuming (dangerous word) that you do not have overheat problem at all when driving. So it's full of coolant, not air bound, thermostat is opening, and the water pump is pumping. When driving, the air comes through the radiator and keeps it cool so the fan doesn't have to come on.
You did say you tried changing heat sensor. Are you sure it was the right heat sensor? I'm sure it has more than one.
In2hoppn (old school but watercooled)