There could be many other things wrong besides the fuel pump. I have a mechanical fuel gauge under my hood after my fuel filter and before the carb, and I have an electrical gauge inside my car as well. Let's just say I have had multiple problems with my fuel system too, so now I know whats up.
I clogged two fuel filters in the first 50 miles of driving.
Gee, what would do that?
So to make this short and sweet, if it isn't crap in your fuel system, it could be a worn pushrod in the block if you have a big block. It could also be a whole in your solid fuel line letting air in. While I'm at it here, make sure the rubber line from the sender to the solid fuel line isn't dry rotted. Then there is the lines up front coming from the solid line...How does that rubber look?