FORD 460 Overheating Mystery

What time was it when you dropped it off at the shop today? Were you in stop & go traffic? If so, you should have definitely heard the engine fan engage at least a few times, especially accelerating from a stop light! I had a `92 Tioga with a 460 for four years, and in all that time in the Phoenix heat my engine fan only fully engaged one time on a Friday afternoon leaving Tempe during the summer. On my temp gauge it had the C & H at the far ends, but spelled out NORMAL in between. When first driven the temp needle would go as high as M(halfway) and would then usually settle between N & O after fully warmed up(one quarter) If I paid close attention, I could hear the engine fan partially engage, but I did have to consciously listen for it! That day in Tempe it got up to A(three quarters) and I think they heard the engine fan fully engage leaving a stop light in the next county!!! If your engine fan is working correctly in 110° heat, in stop and go traffic, you will hear it, especially if you're running the dash A/C. BTW, I did the cooling system flush on that RV also, and did the 70/30 mixture. After a few test trips & seeing the gauge stayed around one quarter, I decided not to add the water wetter I'd purchased. It's been on my garage shelf for 7 years now.
So all that said, I think it's your fan clutch, and also recommend a flush & new thermostat and radiator cap! Wash out the radiator and A/C condenser with simple green, a soft bristle brush and your garden hose. The Ford V10 is bulletproof, but the EFI 460 is only a half step behind:)
Good luck