Ethanol boils at 173 degrees, guaranteed its hotter than that under your hood on a summer day.
The fuel is probably boiling in the bowl and lines.
we have been fighting this on a driven to the track an hour away race car for 2 seasons.
it will pull for the full 1/4 if it sits and cools off with the hood up for an hour or so, but will fold up at the top of 1st gear like it's running out of gas if you try to hot lap it.
If you can get ethanol free 91 i would try that for a few tanks as a test..