The only two choices I have seen for replacement sending units are AC Delco and Spectra.
It is true that Delphi is no longer GM owned. Nexteer (which was Saginaw Steering Gear, then a Delphi company, then Nexteer) is now Chinese owned. The rest of Delphi is on its own, but who knows where the parts are made.
Of course, AC Delco continues to say that they are "The true GM original equipment parts brand."
http://www.acdelco.com/gm-original-equipment-parts.html