Last I knew, the fuel sending unit goes to the PCM first. Just like the oil pressure. It uses fuel level data to run EVAP tests during the OBD2 drive cycle.

I'm suspecting a bad connection at the instrument cluster or a bad cluster.

its not sent separately to the cluster though, its sent with the speedo, tach, temp, over one or two serial data wires, and those other things are working fine

Yea your right Justin, all the data the instrument cluster is getting from the PCM is via the Class 2 Data bus. Which means, the connection is ok, but the cluster is not "processing" the information correctly.