Just my opinion for what it's worth,I'm a heavy line Ford Tech been doing it for the past 15yrs.Like 502 stated no reason to change the temp sensor.
Very serioiusly doubt you have a failed head gasket,I've done 100's of cylinder heads on 4.6,5.4 & 6.8's and very rarely have ever had to do one for a blown head gasket.Usually have to do them for valve concerns,piston inspection,oil leaks,blown out spark plugs.
Triton engines will normally not blow a head gasket and if they get hot enough to blow a head gasket they smoke the engine first(99.9%).Seen that over and over.
That being said i would look into your radiator,fan clutch,t stat,coolant level
I've seen Radiators pretty common where it may have 70-90% flow and only be partially clogged which normally won't affect anything but all of a sudden
it is under certain conditions Heat/towing and needs 100% flow and may have 10,20,30% clogged and puts it over the edge and starts to overheat
and without full capacity can't cool back down.Thats just a thought also check your fan clutch and i would recomend a factory Tstat.
Without having the vehicle in front of me it's hard to say.Good luck and if you have any questions shhot me a pm.