Engine Malfunction #2 Cause Found?

[ABMW]

Started my 35d today with 39 miles until empty showing on the onboard (gas station was closed last night) at 10:30 when I left work.

Started down a steep 10% hill, and all of the sudden "Engine Malfunction, Reduced Power" warning comes on.

This is the second time this has happened. However, the last time it happened I had a FULL TANK of Diesel fuel.

However, when it happened last, it was after parking it on a 10% hill, for about 30-mins., then coming out and starting it.

To me, this appears to be a fuel pump issue. I have 4,000 miles on my 35d and live in the Bay Area where 10% hills are commonplace.

There does not appear to be any type of failure with the fuel pump, as it should either work or not work, in my opinion. But, it appears that the manner by which the fuel pump is placed is not adequate to siphon fuel under certain circumstances.

Or, there's a true issue with the pump, but it's remarkably odd and I'm 100% it's confined to the fuel pump.

I understand it taking place with a near empty tank, but with a full tank?

Luckily, I limped to the gas station, at about 3 miles per hour (literally), filled it with 20-gallons and was on my way with no further issue. I was entirely confident the vehicle would start fine with fuel.

So what's the deal? There were 2.5 gallons of fuel left, but does anyone know I'm guessing there's a gallon tied up in the fuel delivery system at any given time, which would have left 1.5 gallons left.

Still, that's quite a bit and a 10% hill is just not that uncommon, in many parts of the world.

Any thoughts? Similar circumstances on hills, etc.? Has this taken place with anyone on a flat surface with a full tank of fuel?