Andrew - if you would mind opening a support ticket I'll log into your installation and see if I can determine what is going on with permissions.
Normally you should see an additional set of permissions related to Garage when editing a specific usergroup's permissions via AdminCP. If you don't see that then enter the following URL and recheck the usergroup permissions for one of the groups to see if the Garage permissions are visible.
Code:
http://www.yoursite.com/forums/admincp/index.php?do=buildbitfields
Be sure to alter the above URL to reflect where and how your admincp is referenced on your installation.
If the above fails to show the garage permissions please go ahead and file a ticket and I'll quickly log into your site and work to get the problem resolved.
Thanks!
Mark