How do you remove the dashboard

GM was fond of hiding screws in the air vents.  You may need to carefully remove the air vents and look for hidden screws there as well.  I know the Cadillacs I've had of older vintage have all required that.  There are plastic tabs on either side where the air vents pivot which must be carefully pried inwarsd (towards the center of the vent) with a flathead screwdriver and then the vent assembly can be pulled out of the dash.