If everything else checks out OK, you may just need a new radiator. I once had a car that, despite good H2O pump, hoses, correct coolant mixture, etc. it always ran a little hot. It used to be very stressful watching the temp needle in stop-and-go traffic with the A/C on as the car was always on the verge of overheating. At one point the radiator sprung a leak and I had to replace it. From that point on, the car always ran on the cool side, even on a 90 degree day with A/C on high, parked and idling for an hour.

Before discarding the old radiator, I took a good look at it. The fins were loaded with bugs, though not too bad. There was some corrosion, but with the exception of the area that leaked, again it looked pretty good. Inside there was lots of grit, probably from the PO not flushing coolant as often as needed (if ever). I'm guessing all of the above just combined to reduce thermal efficiency significantly enough. Bugs cut down airflow, corrosion and grit inside might have cut down H2O flow through a few of the tubes, at least enough to make a difference.

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08 W251 R350
97 W210 E320
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85 W126 380SE Cranberry
79 W123 250
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75 W114 280