Sounds to me like you're going to have to drop your tank. The pump sits in the tank about 3/4 of the way to the back of the tank. There is a fuel pick up that is in the front of the tank. There is a tube that runs from the pick up and is just clipped to the top of the fuel pump and relies on venturi vacuum to suck fuel from the front of the tank when on a situation that you described. If that tube got knocked out of position from bouncing around then when you are in a downhill and less than 1/4 tank The pump will starve. Dropping the tank isn't bad really just get some help if you are doing out on your back. And don't forget to get a new seal from the dealer or you WILL get a check engine light