Fuel pump issue

[OldChevys]

I'm still kind of new here, so if this is the wrong spot, feel free to move it around (just tell me where it went )

anywhooo.....I have a 71 chevy with a 350 and it is sputtering at highway speeds and under a load. The local carb 'experts' told me to change all of the fuel filters including the one IN the carb (which I did) and it still ran the same. Next , they tell me to replace the fuel pump (which I did) and it still runs the same. I replaced the inline filter with a see-through model and I can see that very small squirts of fuel are making it into the filter, but it is not filling up. I took the fuel supply line loose from the pump and blew air through the line to make sure that it was not obstructed and gas seems to flow easily - gravity flow? I am now lost, but somehow think that maybe there is a flat lobe on the cam that drives the pump? Anyone have any ideas?

BTW this is a 71 c10 350/350 auto

Thanks in advance