I agree with Kevin regarding the clutch install being normal and the transmission install not being normal. Whatever is holding the transmission away from the bell housing is probably creating the release problem - as you draw the transmission to the bell housing with the bolts you are deflecting or binding something that is preventing the clutch from releasing normally.
Are you sure that you are installing the clutch disk in the correct orientation? If it is reversed the hub will run out of spline on the input shaft and get held against the flywheel regardless of the pressure plate releasing it.
