I’m not entirely sure what chip was used. I believe it’s a Schmitt trigger circuit. My wiring guy knows someone who custom makes them on a mini PCB. The problem is that with the magnetic induction sensor, the pulses are too close together and do not rise and fall enough to differentiate the pulses.What converter did you use?
Never been a fan of GPS speedometers. Wasn't comfortable with losing the speed readout in a tunnel (as you said) or the mountains. I know they are an easy fix and for 99% of the probably work great, but just not an option I am comfortable with.
Add that I want to run cruise control and I am betting it will need a signal different than GPS and/or cut out when the GPS signal drops.