1999 Ford Windstar rough idle and heat up

Engine problem
6 cyl Front Wheel Drive Automatic 116000 miles

engine ok most of the time, but, after engine reaches max temp; say and hour or so on the freeway. When I come to a full stop at a light or stop sign or heavy traffic, engine will start to idle rough and temp; gauge begins to climb close to if not to the hot point. If I take out of gear into neutral engine smooths out and temp drops.
or if I start to move forward again it will smooth out and return to normal temp. Cooling system has been power flushed and coolant changed. No leaks of any kind. Freshly tuned, new fuel, air oil filters.
no warning lights on. What's up.