slow boot [or shutdown] after upgrading: Apple Support Communities

Users munsonid and jtownsend251 both helpfully answer. I have noted the cache deleting trick on another post as well to fix shutdown issues.

To repair permissions

a. open up Disk Utility

b. click on your hard drive (Macinhosh HD)

c. On the right hand side click on Repair Permissions.

To delete caches:

from the Finder’s Go menu, choose Go To Folder.

Go to this folder: /Library

Delete the Caches folder.

via slow boot after upgrading: Apple Support Communities.