Cylinder size is 60 probably - not sure though.
Yes i saw this thread earlier aswell.. but was looking for somebody who has faced this issue personally and resolved it.
Earlier i had a 2006 Gli and remember having the same problem with it too.. any ways i'll check this up tomorrow morning, hope i get to the idle air control valve - and get this rectified.
and yes, i get 150 to 155 with 8 to 8.5 Kg gas in my cylinder. this figure i quote is not exaggerated. Can share the trick if you'd like to know it. for sure.