Long load times, waterfall issues, with DomainMapping.

Does anyone know why .../wp-admin/admin-ajax.php?action=domainmap-setup-cdsso takes up so much time on the waterfall? The homepage is just 165Kb but 2.19s of load time is required by the SSO. Any suggestions?

http://tools.pingdom.com/fpt/bjUrSj/http://tcbok.org
http://tools.pingdom.com/fpt/eGrvC/http://tcbok.org