If I'm remembering your shop location correctly it is right at sea level, correct?
I have seen the density altitude at Thermal airport(150 Ft. below sea level) be right at 8700 Ft in the mornings in June, I have also raced at the old street races in Indio in March when the D.A. was probably around 1200 Ft. shruggy
The motor knows how thick or thin the air is regardless of the Pro Charger, correct shruggy

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)