my old grand prix gtp had a digital boost gauge stock, the ATS should have had one as well.
I have AeroForce Interceptor gauges in my Camaro , they plug into the OBD port and can read many man different paramaters. Each guage displays two digital readouts at one time. So if you mounted one on the Caddy you could be viewing boost and oil pressure at the same time. finding the right spot to mount it is the hard part with these cars.