The reason why I doubt your diagnosis is the fact that the PCM should detect a problem in oil pressure sensor and code it.
See ACE0 attachment to see what I mean. Normally on these engines, if memory serves right. If pcm does not get signal from oil pressure sender, it shuts off injection/spark. I could be wrong and getting mixed up with other gm's. Maybe another mechanic member will chime in.
You should have a code similar to this if sensor is actually malfunction or something is amiss in the circuit.
P0521 Chevrolet Description
The PCM continuously monitors the engine oil pressure. The Oil Pressure Sensor/Switch sends a signal to the PCM when the engine is running.
Read more: http://engine-codes.com/p0521_chevrolet.html#ixzz3KPBeoihf
I went with a 4.8l since I don't know what v8 you have. So specify so I can post proper schematics.
I added a flow chart for a P0522 code EOP sensor(engine oil pressure) since this one applys to a 4.8l 2003 chevy. ACE2 attachment.
While very unlikely but not unheard of, this could go to a PCM replacement. Thus my preference for a mechanical gauge.
You can buy an adapter and have both oem electrical and your own mechanical gauge. Something like the picture I attached.