Overheating....again

[ipd]

So I had the Head Gasket replaced circa 2016. Haven't had any issues with it until now--including a cross-country trip in 2017. Temp needle has been bang center the entire time. Today? It's pinging hot. WTF. Ambient isn't terribly hot yet. 80 maybe. Nowhere near as hot as it was in Phoenix when I first thought I'd had a problem.
Any ideas?

[ipd]

Well after watching the temp needle go from normal to high end to normal--all while doing nothing...and given the disparity in temperature between the two hoses coming out of the radiator...I'm going on the hunch the thermostat is shot. Having it replaced tomorrow. Not cheap...but hopefully that fixes the issue before I'm out ANOTHER head gasket.