Are you capturing the execution plan in the 2008 version of SSMS? Make sure you have the latest service packs installed on your server and on your client machine. Check the default settings for connections on both to ensure one isn't different than the other. After moving the database, you need to update statistics. If not, they get updated manually. Try updating them with FULLSCAN on the 2008 server to ensure you've got the best possible statistics. Not being there it's hard to know, but no, I've never seen any differences in execution time for queries run from 2005 or 2008 versions of SSMS.