04 300m overheating issue

Yesterday evening, I took my wife to some women's seminar about 15 miles from our home in my 04 300m. When I was leaving I noticed the temperature gauge was higher than normal(about half). The fans were running and so was the a/c. When I pulled into the garage I shut off the a/c and the gauge rose just above half. Coolant levels are fine. Checked for leaks, couldn't find any. 75% stop and go traffic, 25% highway. Water pump? stuck thermostat? Water pump/Tstat/flush done 10 mths ago. On the trip to pick my wife back up the temperature gauge stayed normal. Approx 1 hour later from dropping her off. Thanks

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