Interesting... $85 / $D8 have the ability to guess at which sensor type is installed. The data word at $0043 contains a status bit for the type of sensor currently selected. If code is set to guess at which type of sensor is present, and the code does not see one type of speed sensor signal present within a preset time after selecting one type of sensor it will toggle this bit to select the other type.

The mode word constant at $900A has three bits related to speed sensing. Bit 0 selected indicates TISS input shaft speed sensor installed. Bit 4 selected indicates output speed comes from DRAC sensor. Bit 7 is used to indicate the code should guess at what type of sensor is being used. BAMW, AWAY, and AXXZ are both set to $80, "Guess at speed senor type." Setting this bit to $20 will deselect "guess at speed sensor type" and select "Output speed from DRAC sensor." This could solve the switching VSS issue. Optionally, changing the value at $9039 from $28 (one second) to $50 should effectively double the window before speed sensor type is changed.

Without the ability to burn or replace the chip, I would likely test VSS signal for consistency while driving by scoping the VSS signal line within the PCM. As noted, you should see no pulses for over one second before the signal type status changes.