I still sustain that a fuel pump problem can be the culprit. Fuel pumps can and do become temperature sensitive. I had a pump that would work fine driving around town, but when it was a hot day over about 95 or higher, the fuel pump pressure would drop and it started making a strained noise. The noise wasn't always there, but the symptoms were consistent with yours. Mine required hotter ambient temps to show up, but the issue is about the pumps internal temperature. It can get hot enough internally to misbehave without the outside air being hot at all. I would hook a fuel pressure gauge and see what is happening while this problem is occurring and see if the pressure drops when this starts to happen.