Sounds like you've might have a hole(s) in the gas line.
When the pump tries to pull gass from the tank, there is no suction.
You haven't noticed any gas on the ground, becuase liquid, normally doesn't run up hill.
Take a look at all you lines running along the frame, I'll bet you come up with your problem.
Chris (Mazda4X4)
PS You might want to check out the new board -
http://www.mazdatrucking.com/cgi-bin/ikonboard.cgi. Ken (Kryasis6) has moved everyone there.