Starving out on hills

[studeclunker]

I have an old crate-350 in a '66 Camper special C-20. When I start up any kind of hill it is starving out and just about stalls out. I can back it up the hill (like a tin-lizzie) and the truck runs smoothly. Going forward (uphill) though is just not possible.

It has an electric fuel pump, works well, as far as I can tell.

I put a new mechanical Fuel pump back in and still have the same issue. Tried it with the electric and with the electric by-passed. It still does the same.

Pulled the sender/intake module from the tank and all appears to be fine. The brass fuel screen cylinder is in beautiful condition. Amazing considering its age. So there's nothing blocking the fuel supply. Would water in the tank do this? That is to say, run fine till I attempt a hill?

Found out why my fuel gauge isn't working. The ground was broken. Fixed that when I put it back together. I'll replace it with a new wire later.

So I'm stumped. Any ideas of what else to look for?