I think you have done a good job covering all based on the easy stuff.

The next step should be the tank strainer. It may be full of gunk that slows the flow of fuel at high speed, and, after 10 minutes or so, the engine begins to starve.

Jim recently posted a photo of one of his strainers. Unbelievable that the damn thing ran at all. He did not have any algae in the primary that was apparent.