Finally got under the truck and took a closer look
First, the problem was isolated to the left rear sensor and/or common wiring. Moving sensors around did not change the symptoms or indications.
Finger over finger tracing of the accessible wire runs exposed a problem that requires attention and certainly could be the cause of my issue.
There is a connector plug with six wires for the rear PDC array located at a right side plastic bumper cover support approximately six inches inboard of the right exhaust pipe.
It's supposed to be retained by a sliding clip on that support but mine broke away some time ago and so bent some of the wires severely. Since it was resting on the wires it looks to have worn away the insulation - the intermittent problem - and eventually corrosion took hold and now there is no conductor material left, causing the permanent fault. It's a YLW/GRN tracer wire which is the wire color at the left rear center sensor.
It's too close to the plug to do a proper repair so I'm hoping the entire plug is available. I've included pictures so that maybe one of you can help find the part.
