Cool man thank you
To replace the temp sensor does any of the belt need to come off or can you get to it without touching the belts?
Without walking out and looking at the car, I'll say no its easily accessible without remove the serpentine belt. I certainly was able to easily undo the electrical plug from the sensor the other day to test the slow/high speed fan circuits.
Even if you find removing the belt necessary, no big deal. Just make a front on drawing of the way it goes around each of the pulleys before you remove it. That's the only hard part, figuring out how it goes around the various pulleys when you go to refit it. To remove it is just a matter of fitting an appropriate size ring spanner on the tensioner pulley nut and levering it back to remove the belt tension, then just lift off. Refitting the same procedure. Just make sure the belt sits centered on all grooved pulleys when it is refitted.
And you will need to bleed the cooling system from the bleeder in the top of thermostat housing after changing the sensor. Just need to remove the plastic engine cover (4 nuts) to get access to it.
P.S. And the reason I think its most likely the temperature sensor, or if not the thermostat, rather than some of the other suggestions, is because the engine temperature returns back to normal quite quickly. The only reasons I can think off for that happening are the fans finally kick it, or a faulty thermostat finally opens. Every other reason for overheating that I can think off e.g. blocked radiator, low coolant level, cracked head, etc, etc, .... this wouldn't happen. It'd just get hotter or stay hot. That it quickly returns to normal tells me the 'bones' of the cooling system are fine. It's just something not kicking in early enough before the temperature gets high e.g temperature sensor, thermostat.
PP.SS. Maybe just replace the thermostat while you have the engine cover off anyhow. What are they $25? Only one coolant top-up. Downside, you'll never know which it was if changing both fixes the problem, perhaps you don't care.