This is not a carburator. Fuel injection needs the full 29psi pressure. Up
hill or down shouldnt matter.The amount of gas in your tank may matter.The
fuel outlet on the tank is at the rear of the tank,so going down hill will
push the gas to the front.I would suggest a large filter after the fuel
pump (in addition to the one infront, and like the 86 and later vanagons).
In addition to extra fuel filtering,it will hold a large quanitity of
pressurized fuel for long lown hill treks. At least half a pint or more.
Just my guess.