Seems to me that steps 5 and 6 are in the wrong order. You need to verify that mail is flowing driectly to the destination server and not through the source server via the routing connector.
go.microsoft.com/fwlink that's the exact steps as per that. At this point in time you've already run the wizard to set up email on the new domain. All you are breaking are the mailbox connectors between the old server and the new server.
This Exchange blog entry is the best thing I've ever seen! This document made what has been a very painful transition in the past, VERY EASY! This thing is awesome! I actually pdf'ed this in the event that this blog ever changes! Susan and Ed, you are my idol!