Runs fine, but not a stops

1996 Caravan, 2.4, runs fine on open road with no problems. When you get into stop and go traffic, now the problem starts. It wants to start overheating. It will eventually peg the gauge! But before that happens, I turn the heater on, and it kicks the fans in and starts declineing. Does this vehicle have a relay problem or a coolant temperature sensor problem? If it has a relay, where is it located? I know where the sensor is.

Do the simple/cheapest thing first. Replace the thermostat and gasket and go from there. Don't keep overheating. You will ruin the head gasket.

OK, changed the Therm., same thing..Still wants to climb the temp gauge and fans will not come on. Went to AutoZone, had them lookup to see if there was a reley for the fans, they said No. So then I went for the Coolant Temp Sensor, Yep, they had that. Got that, took it home, and guess what, Doesn't fit any connection I have. It should go just to the right of the Therm housing from what the Childons book says, same place for the V6 models. In fact, I have the same connector and what appears to be the same looking sensor on the right side of the Intake with the same type connector,. Won't fit there either. Took it back and they rechecked it again and swear it's the right one. Now looking at the recalls and the TSB's on this thing, TSB 8251 and 8252 list a recall for the FAN Relay, OK so why am I told there is no relay if there is a TSB? Did they modify the housing and change this sensor to a bigger one?