Had a similar experience this Summer in Texas.
When I built my generator compartment, an additional squirrel cage blower was built in to kick out excess heat if needed.
I have never had to run it due to high engine temperatures, but have run it when stopped to assist in heat removal(keep it from rising up toward the cabin).
Well, this Summer before our Texas trip I did a little redesign in the gen compartment and pulled the fan out, but, running behind schedule never put it back in.
I swear this started the second we crossed the state line, but can't be sure. We stopped at the welcome center and when we came back form walking the dog I noticed the genny was off.
My Kubota has never had a problem in any season with outside temperature, but the temps were 105 today. Long story short it needed the extra blower to stay cool when stopped in these temps, ran just a few degrees hotter from normal when moving.
Yeah, the blower is back in now.
And I never had an issue once we were out of the 100's on the way home.
I agree with Bob that I would verify that your reading is correct first, and a lot of other good idea's, but it just may be an air flow/removing heat issue with the temps so high.
Best of luck on your fix,