Fuel pumps are always better new because internal parts dry out in junkyards if they have been there awhile. If it's mechanical, it's relatively cheap anyway. If it's electric they often take a long time to swap so I wouldn't risk a used one for the work it takes to put it on. If multiple ones have failed I would check them unhooked and maybe change fuel filters.
Most likely, yes, if that is the problem. There are too many other fuel line problems that it could be to list here. Did you change fuel filters? Could injectors be clogged? There's just no way to answer without more information. Best of luck.
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