Can you tap into your vss with a battery powered oscilloscope? I just got through chasing a similar gremlin out of my van.
Mine was an intermittent in the PSOM. Solved by a replacement from eBay.
One thing I did see was my rear end was beginning to wear, and the vss sensor, which is magnetic, had attracted a lot metal filings, which were shorting the magnetic field the sensor uses to see the teeth of the tone ring.