I'm fairly certain there needs to be an "ARM/lockout" switch somewhere so the TCU knows whether it's in autostick or automatic mode. My dumbed down schematic does not take that into account. In a real autostick car, the gear shifter MOVES OVER into a new track, that has up and down. That screams switch/relay to me.

The whole selling point of autostick is that you can go to redline before shifting... and downshift to slowdown early. If the TCU doesn't see a lockout signal, it won't wait to shift... just shift when it wants to.

I think if you hook it up as I drew it with 2 momentary switches, you'll find you can probably upshift early, but not late, and probably not downshift at all. It's a start.