2000 Caravan overheating problems.

I have a 2000 caravan w/ 3.3 V6. My engine has started to overheat when the a/c is on in top/go traffic. As soon as you shut the a/c off the temperature goes right back down.
I have checked the fan(s) and they seem to be working properly.
Could this be a thermostat issue??
Thanks for the help !!!

Could be several issues. Start by checking the operation of the cooling fans. Start the car with a cold engine and turn on the A/C. The fans should come on right away. If they don't, you've got a problem. If they do go on, you could still have a problem with a coolant temp sensor, or a fan relay. The fans are two speed and perhaps they're not kicking into high speed when A/C is on. A bum T-stat would probably give you problems even when the A/C is off.

The fans are definetely working i checked them under hot and cold conditions. They seem to be operating correctly. I neglected to mention in my earlier post i was a little low on coolant (no leaks) but i don't think that is the issue.
I will try the temp sensor. I may try the thermostat its cheap/easy enough to do and it will at least eliminate that possibility.
-thanks