Ya, that's what I meant by pickup. Well if the tank is that clean, I would say your electric fuel pump is at fault. It sounds like it's overheating, and when you add cool gas, it keeps the pump cool for a while. Your regulator shouldn't make a differnce hot or cold. It's just a diafram. Now vacuum to the regulator(if yours has vacuum), or a pin hole leak in it could cause problems, but my guess is the pump.