I'd say it's the downward slant. On a '95 model, when I used to get low on fuel, my engine would shut off whenever I applied the brakes. I guess the fuel pickup is at/near the rear of the tank?
Keep it above 1/4 tank--all the impurities in the gas settle into that (or is it an old wives' tale?) More; when you park you vehicle without alot of fuel in the tank, the changes in temperature over the course of day (and especially night) can cause condensation and water in your fuel.