2016 Chevy express 3500 overheated one time only

What is your question?

Van was in park and overheated suddenly. AC was running and memo came on "overheat AC off". I turned AC off and turned van off for a minute. Continued to drive in stop n go traffic with AC off and did not over heat again. Over flow Fluid reservoir was a little low. Refilled with proper anti freeze and drive van later on. Since then van runs at temp 210 and appears to be fine. Had the van checked out by dealer and they said radiator needs replacing. Van has 74k on it. Dealer appeared sketchy and non convincing that it needed radiator. I declined repair. Have driven van and cannot get it to over heat. Any ideas?