Look up Aeroforce gauge. It plugs onto your code port (OBD) inside vehicle under drivers side dash.
I have had one for over 6 years in my Twin Turbo Lincoln. Works great and has many other advantages/options. My Caddy has a factory gauge, otherwise I would probably add this. As for the Buick, it's my wife's and it's not important enough (ok not even on her radar) to her for me to get one.