Truck began to overheat in drive thru with A/C maxed.

Hi, as the title says, i was in a drive thru with my AC maxed out and the temp gauge began to rise. It hung around the 3/4 mark before i realized due to the fact that the AC began to blow warm and i turned the AC off. As soon as i turned the AC off i watched as the gauge dropped back to normal operating temps. I drove another 30 minutes in stop and go traffic with my AC on with no issues and the temp remained normal. I am currently sitting in the parking lot of my destination for the last 30 minutes with the truck idling at max AC with no issues.
So what gives? What could have caused the temps to rise so drastically for that short period of time, only for the temps to go back to normal as soon as the AC is turned off? I can’t replicate it just yet but i will update if i do.

i just finished driving 2.5 hours and its about 100F in TX right now. 0 issues the entire drive, in fact this is the first time anything like this has happened before.

coolant was flushed at 100k, im sitting at 120k, oil is at 3k miles with zero leaks (penzoil plat high milage), radiator is clean, no coolant leaks.

 

Hope it was just no airflow into the front grill if behind a Suburban, a common TX problem.
Others could be thermostat starting to stick but doubt it if OK rest of time. Cap not holding pressure. Fan clutch failing freewheeling. Is the fan shoud on. Any screen over the front grill for bugs that got dirty/clogged.
Then if your AC pressures low or compressor if starting to fail or the clutch but AC would normally not work then so doubt that. Not an AC guy.
Make sure air filter intake is clear at pickup in fender maybe paper flew up in there never know then got sucked thru to filter so open and look.
Long hot line no airflow I hope.

 

The only time I've ever seen something like this is when there was a bubble in the cooling system and once it was "burped" then the system went back to normal.

But 20k of driving after a coolant flush SHOULD have burped out all the bubbles. If you want to test it out, find a way to incline the nose of the truck (jackstands, driveway, etc), pop the hood and have someone observe the overflow reservoir and then lightly apply throttle (do this after the engine has warmed up enough to open the thermostat). The incline makes the radiator/overflow the highest point in the system and air will migrate there and you'll see it literally burp out the bubble.