Greg,
From what you have described and what I get from the books, it could be the hall sensor.
The 8 volts when your looking for 3-6 concerns me but maybe the meter is off a bit.
I had an intermittent ignition problem some years ago with my 780 w/'89 5.0 V8. The car would cut out at any given time and would start bucking. After a long frustrating period of troubleshooting I found there was an intermittant grounding of the IDM lead between the TFI module and the engine computer. That intermittent ground would take out the coil signal and tachometer which are in the same circuit.
I cut the lead at the TFI and at the ECM and ran a new wire. The car is still running today with my home made BYPASS setup.
So if everything is checking out per the book and the code is saying "Intermittent PIP Signal", you may have an open or short in the harness somwhere between the TFI module(PIP) and the ECM(pin 56). You could easily run a new lead from the TFI and in thru the door to the ecm as a test. It wouldn't cost you anything. Worst case, you'll have to resolder the cut wires back together.
Steve