You generally see this in city driving but its not impossible to happen at highway speeds. Generally the fans kick on and help pull out some of the heat. At highway speeds the fans wont turn on but there should be enough cross wind. In 108 temps and possibly even higher due to the road temps being higher then the surounding air due to the sun beating down on it all day that can be enough to tax the system if your running the AC.
The AC started working normally again later.