Based on what you described and the mileage, I would guess that the screen on the pump is somewhat dirty, and when you are on the slope, the fuel pushes far enough forward causing the problem. The pump is aprox in the center of the tank. If the filter has dirt in it, it may not pick up the fuel if it is too low on the screen / filter. I bet if you were to do a volume test when it was in that position, you would find it is lower than minimum requirements.
The only way to be sure would be to remove the tank, remove the fuel pump and check it over and see if there is dirt in the bottom of the tank. If it makes you feel more confident, I have a 2000 Expedition. If I have less than a quarter tank and start the car to warm up on my slight sloped driveway pointing up hill, it will run out of gas until I coast it back on to the level. However, I have never had a problem with the pump other than that issue.
Let me know if you have other questions.
Wednesday, March 4th, 2009 AT 10:15 PM