I agree with GNS... Your return line is being cutoff by something.

I would put my money on it being a vacum issue. When there is a drop in vacum the regulator closes the return line which gives you a boost in fuel. So it could be since there is low vacum the regulator is cutting off the return line so the fuel builds up in your fuel rails which is causing it to cook and get boiling hot and thats why when you check your schrader valve you have gallons of hot fuel coming out.

I would check out the vacum first if that just happens to be good then check out your regulator the spring in it probally got stuck and thats whats cutting of your return line and causing all your problems.

Hoped this helped! Let me know what happens!!