[Big-Foot]

Most vane type pumps will not be long lived in a position where they have to suck the fuel up-hill. The manufacturers all indicate that the preferred mounting position is no higher than the top of the fuel tank/cell..
The old SW pumps were diaphragm pumps and would pull fuel straight up 30 feet. I don't know if your pump has failed but it sounds like it's check-valve may have some crud in it or the vanes are just too fried to seal up anymore..