So I have an 03 Yukon XL, 5.3 flex fuel. While I was out of town the wife ran it out of gas. I've added 5 gallons of gas but no start. I can hear the pump running for a few seconds and what sounds like a lot fuel returning (splashing) to the tank. I squirted fuel in at the throttle blade and the engine runs until the fuel is gone. When I push the shradder valve in there is no fuel at the fuel rail. I've owned the truck for 18 months and replaced all filters when I bought it. Could the regulator be malfunctioning and returning all the fuel to the tank? If so, how can I test that? It pulled a code for MAS but I think that is because I disconnected the intake plumbing to inject fuel at the throttle blade. Maybe I should just start with disconnecting the fuel line at the filter and see if fuel is flowing there. Maybe the fuel was so low it lost prime. Shouldn't it gain prime easily after adding fuel? I'm grasping for answers here but i guess I'm going to have to push this heavy beast to my shop around back and get under it. Thoughts from others? Thanks in advance!