Something is a little off there. 210 is in the high normal range. I'm assuming that you're saying that when on the move the temperature will drop, but when you're idling that it will go up. One suggestion: I know my 2004 Silverado had a mechanical, belt driven fan with fan clutch. It's possible that the fan clutch is starting to go and not spinning the fan FAST ENOUGH at idle. It might be spinning it some, but not fast enough to meet spec. That might be worth looking into (all of that is out the window if your Express has electric fans). Also, it might be worth taking a garden hose, opening the hood, and spraying the radiator off from the inside out to get rid of bugs and debris. You'll be really surprise how much junk comes out of there, even if it doesn't look like a lot. These are some simple steps, but sometimes they are the ones that do it. I will say that my 2004, even in perfect running order, heated up running the A/C in Winslow AZ while sitting still at a post office. It was about 105 or so at the time.