Originally Posted by phunk

I am going to guess that the fuel level sensor is on its way out. When mine was going out several years ago, it would intermittently shift between 2 positions about 1/4 tank worth apart. Sometimes hours apart, sometimes not long at all. Sometimes it would read full tank when I filled it, sometimes it would read less than full.

There are those fill valves on the bottom of the canister.. on level ground it would only take maybe 1", if even, of fuel depth to get to the fuel pumps. So if the tank was quite low, it would be no surprise to have fuel pickup issues on a steep hill since the fuel pump mounting flange is about in the middle of the tank (front to rear) and so is the venturi pickup on the driver side. But since it sounds like it didnt want to run even on level ground until you added fuel, I have to assume that either the tank was legit empty (level sensor reading optimistic), the check valves are blocked (unlikely with such a new installation), or perhaps the fuel pumps are too high (i have seen people slide them all the way up in the pump holder rather than setting them so the pickups are as low as possible)