vent line for fuel tank plugged?

[1972BackInBlackC10]

was wondering if the vent line on my truck was plugged if it would cause the truck to die? seems like its losing power and if try to feather the gas pedal or floor it the truck will die either way even if yu just take your foot off the gas, the truck starts fine and runs fine but a soon as you get a certain distance it does this, iv basically replaced everthing there is that could cause this problem nd im about to put in a new fuel tank does anyone think it could be a plugged vent line or possibly mixed up return and feed lines as my friend elimnated the second fuel tank nd possibly hooked them up wrong