Conversions & Hybrids - Climate control issue

I have an 02 ws6 and ever since I've owned it it has only blown air out at the floor and the center defrost in the middle of the dash it's not the switch because it will still turn the air off but no matter what position you put it in to blow out it only blows out at the feet and middle dash. Im 99% sure it's not vacuum because it does it all the time not just on acceleration. Anyone know what the problem might be?

Welcome to LS1tech! SEARCH will be your best friend.

It does sound to me like a vacuum problem. Start by checking the vacuum check valve and it's hoses/lines:
http://shbox.com/1/vac_check_valve.jpg