[StevePT]

Your problem is not necessarily under the dash. There's a vacuum line that runs with the electrical bundle on the passenger side of the frame in the engine compartment under the battery. Trace that vacuum line and make sure it's not cracked anywhere. This is 9/10 times the reason for the mode selector not working on the W-Body vehicles.

As far as removing the center console, no you don't have to remove the shifter. The console has a couple screws holding it in towards the front under the ashtray and then in the console lift out the CD/Tapes/Junk holder and below you'll find a couple more screws to remove. Once those are all out you can lift up on the center console and move it out of the way.