Actually, I would have said 40mph, but it still rings true. Of course the condenser of a high capacity A/C system can affect that by pre-heating the radiator air significantly. Assuming the thermostat is working correctly, I would do my best to verify that all the veins in the condenser and radiator are clear of debris and dirt. I'll take a garden hose or pressure washer to mine at least a couple of times during the Summer months. Also, verify that the coolant is clean and reasonably fresh. If anyone has added tap water, that could cause long term issues. Has the cooling system ever been cleaned and flushed? There are many bases to be covered.
One additional thing I could mention is I understand that there are many that preach only Motocraft parts, but many aftermarket fan clutches have lifetime warranties. O'Reilly has been great at simply swapping parts at no charge when I've had issues. If it was purchased using your phone number they don't even require a receipt. Lifetime warranty can be important. I just replaced all 4 of the struts on my 2011. That's a pretty fair chunk of change that I will never have to pay for again.
The radiator has been flushed...gets it once a year. I usually check and clean the rad & condenser coils if I have to remove the fan, shroud, or anything that actually lets me get in there. Interestingly enough, I cleaned everything when I replaced the fan clutch this morning. I didn't want to think I had to replace ANOTHER one, but I finally accepted it. It ran slightly warmer while on the interstate, but nothing worth talking about. However, as soon as I hit stop/go traffic, she started to climb. For reference, the dash gauge doesn't start to move until the engine hits about 220F.
After replacing the fan clutch this morning, I drove around for almost 2hrs in 93F heat/humidity. She never got above 202F, and that was only after sitting in traffic for 20 minutes due to an accident. Running 75-80mph she never got above 197F. So as much as I did not want to believe it needed another fan clutch, it apparently did. My only concern is I did not go with Motorcraft this time, and the unit is smaller than the Motorcraft unit. So we'll see how long this one lasts. I still need to hook up a trailer and see if she stays cool pulling a load.