Auto or manual? If it's auto, and it's shifting normally, that would suggest the trans computer knows what's going on even if the engine computer and gauge did not, which might help narrow it down. If it's manual, well, there's that theory shot.
And, yeah, go get the '97 manual from Nicoclub. Should be some troubleshooting or at least a circuit diagram in the EL section. There's a lot of hand-holding for using the special dealer Consult tool, but there's usually an alternate method for the rest of us. If the sensor is good (and so is the gear that drives it), and both the cluster and the computer say they're not seeing anything, that would have me looking for a wiring fault in between them.