[ls1nova71]

I think you're right, it's unlikely that both sensors are bad at the same time, and if everything else has checked out, it would seem to me it would come down to a wiring issue. Before we go there, Have you double checked all the harness grounds? Remove them, clean them up so they are clean and bare metal, then bolt them back on and make sure they are tight. If that has been done, check the fuse again, and specifically the terminals where the fuse plugs in. Just testing the top of the fuse doesn't always work, because you could have a good connection on the power side, and through the fuse, but maybe not from the fuse to the other terminal.

The power wire is really the only place the heater portions of both sensors are connected, which is what makes me think the problem is on that circuit. You could also check for power at the O2 plugs to make sure you actually have power there, it will be the 2 pink wires.