I tried using an aftermarket fuel pickup sending unit once, and ended up having a ton of issues getting fuel to flow. Apparently the sock kept collapsing down when trying to suck fuel out of the tank. I cleaned up the original sock off my old sending unit and reinstalled it. Been fine since, and that was a few years ago.
Casey
1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter