We live just outside of Tucson (year round), so +10 on adding a Scan Gauge (or comparable display). As noted Ford (and most other manufacturers), install dash gauges that tell you what you think you want to hear/see. I always run with my SC displaying coolant and trans fluid temps along with average and real time mpg.
The dash gauges may be right in the middle but the SC will tell a much different story. When the trans fluid temps begin to climb it is time to engage the Tow Haul (or turn off the O/D), to enhance cooling. Doing so can lower that temp by 10 got 20 degrees in just a couple of miles.
I have seen the temps of 110 to 115 in June - August but that does not happen until the late afternoon which is always the hottest part of the day. I can't begin to imagine just how hot the asphalt gets. :E
We like to get out early when the temps are more reasonable and as we rarely drive more than 6 hours an 0600-0700 departure will assure us of reasonable temps even in the Arizona summer. Works for me.
:C