Phil, As I am sure you know Ford gauges are notorious for being glorified idiot lights but fortunately there is nothing deficient about the ECM. By tapping into it through the OBD port the Scan Gauge gives me all I need and much more.
This last trip was typical albeit a tad longer than most at 4,150 miles. Most of it was either deep in the Rockies or cruising down the interstates at 65 - 70 and the usual trans fluid temps were 186 unless I was climbing a lot and then it would get as high as 212 - 216. I saw 225 once climbing up out of Panamint Springs in Death Valley in September with temps at 110 and that was towing the Harley
Coolant temps typically sit around 198 but will climb to 210 -216 on extreme grades or if the desert heat is cranking. No harm or foul as they both drop like a stone as soon I reach the summit or take my foot out of it.
Towing the Indian in my Cargo trailer {bike and trailer weigh 2,200#} this trip we averaged 9 mpg. Saw higher {long downhills} and lower {driving into 35 gusting to 50 mph winds right on the nose for hours at a time}. I can't say enough good things about that V-10... it is a beast that has never even flinched.
If I had to guess I would say your previous lack of religious use of Tow Haul contributed to the shortened working life of your original trans which is pure conjecture on my part{not to mention that your hobby is to fill the rig up with lots of rocks and go where few would follow}.
:C