Are you sure the ALL the clutch teeth are aligned? Perhaps the last clutch is not aligned and won't let the inner part sit down all the way. I remember mine sitting all the way down on a 1982 C5 I did about 6 months ago. On a 1968 C4 I worked on prior to that, the clutch teeth were bent and I had the problem you are describing. I did not rebuild the 68 C4... it was my practice one which is now parted out in boxes and bags in a garage corner.
