Fuel Delivery ???? Gas tank issue

[chopnchaneled]

Just recently got my 68 stepper on the road and everything was going great untill sat, evening when it quit running.

A little back ground on it:
I installed a late model 350 engine that does not have provisions for a mechanical fuel pump. Installed a electric pump on the frame rail as close
to the tank as i could, have put several 50 plus mile trips on it since.

When it quit could hear the pump running like it had no gas, the see thur filter was dry.

Took the gas line loose at the tank, drained approx. 15 gallons of gas out.
checked the electric pump,it would pump out of a 1 gallon jug.
put 5 gallons of gas in the tank, still puzzled as to why it quit? Well the pump would not prime out of the gas tank, Pulled the line loose at the tank and NOTHING would come out even with the 5 gallons i had just put in even though i had just drained out 15 gallons thur the same tube.

My question is what is going on? how does the pick up work in the tank?
by the way there was no rust or trash in what i drained out, and the engine will start right up and run with a rubber line from the pump in to a gallon jug but will not hooked to the tank?

HELP PLEASE, I'm stumped.