I had same problem.
Mine has an integrated inverter with 2 grills on the ends and a fan on one side, it’s part of the generator, it’s not 3rd party. mine is mounted in the storage box next to it. I had folding chairs packed too close to it and it was over heating and shutting the generator down. I tried EVERYTHING you tried until I discovered this. I cleared the area out and it runs all day in 95 degree temps. So simple, but I just didn’t see it.