Ok, I've hooked up one of them to Aux VSS+/Digital Freq IN 3.
In TunerStudio, I set it up in the Speed and Gear Sensors page, with appropriate tire diameter and tooth count.
I copied the MPH gauge to a new gauge and assigned it to More Gauges -> Sensor Inputs2 -> Vehicle Speed Sensor 2
The gauge item is red and I get no reading. Is there a feature in the software to watch that input directly?
With my car, it disconnects around 20 feet away.
Holy crap! That looks complicated.
I'm anxious to see some logs from your setup, if your main VSS is the stock speedo input, then an old speedo cable can make that input a bit jumpy (mine is really bad...). There are some VSS sensors that can mount right at the transmission that would improve that immensely.