How is your radiator? No blockages? You reversed flush this - I assume - when you flushed your coolant out?

Why I mention getting your system pressure tested is that the water pump may be not working properly and circulating water around the system efficiently enough.

The temperature in my city reached 115 degrees last summer. The temp on my 103 reached around 110 degrees - at highway speeds. This was with a leak at the water pump (since repaired).