Intermittent Fuel Delivery Problem

[rushingad]

I have been having a problem with the fuel delivery on my 72 K10 pickup with a 350ci. From what I can tell, gas is getting to the pump but not the carburetor when the problem occurs. The weird thing is that it may work for a week without a problem, but then one day it will just stop sending fuel to the carb, and may start back within 30 minutes or so of trying to crank and putting gas straight in the carb. I think it may be trash in the gas tank, because those old mechanical pumps usually either work or they don't. However when I pull the fuel line from the inlet on the pump, there is fuel coming out. It's not a ton of fuel pouring out but there is some fuel coming through the line.

Any Ideas?