Old or New Fuel Sender?

Had the factory sender in my demon and about a year after the resto it went, bought a aftermarket one recommend by guys on here, supposedly its the closest to oem for being a aftermarket, ive not been happy with it, my oiriginal sending unit showed exactly how much fuel, the aftermarket one seems to read 1/8 of a tank more than there is, i would love to locate a nos one.