Pressure is actually after the pump so it wouldn't matter the pressure in the tank itself. If it did matter then you would have problems starting your car after filling up at the gas station with any car, or you would have to pressurize it before starting. When you are going to start your car, the pump goes on to pressurize the fuel rail before starting, and as a by-product your gas tank gets the vacuum affect. The pressure is due to the pump creating a lower pressure in the tank by sucking the gas and sending it to your fuel rack. Since the gas cap is present, the low pressure in tank cannot be equalized by to atmosphere therefore you get that sucking sound when you open your gas cap.
I think its your distributer because it has 3 important sensors, and the icm. if one sensor goes bad it will give you a wonder of a problem that me seem elsewhere but the distributer.