Fuel Filter Empty in the morning!

[Tillik]

This has happened 4 times since I've owned the truck. Approx 3 months. My Driveway angles downwards into my garage. So the truck is parked on a slant most times. The Truck turns over very strong and cranks and cranks and cranks. When I pop open the hood the clear fuel filter is empty. Even tho I crank it several times, the fuel doesn't seem to make it to the filter. I use my generic pump and connect it to the filter. A few pumps and the fuel gets to the filter. Reconnect and fires right up. Don't see the issue for a few weeks.

Truck Info - GM 350(Old), New Carb, Intake, New Fuel Lines-Filter, New Behind Seat non-efi Fuel Tank. No obvious fuel leaks in the line that I can find.

I'm going to change the fuel pump out because it's the only item left in the system. Does the mechanical fuel pump have a valve that would maintain fuel pressure when the engine is not running? If so, should I be able to suck the fuel thru it without cranking the engine. Any input would be awesome. If the new fuel pump solves it, I will eventually post a follow-up.