Sql Server Performance Degradation in moving from 2005 to 2008
Did you rebuild indexes and statistics after setting up the database on SQL Server 2008?
It's mentioned on MSDN (see &quot;Next steps&quot;)

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Next Steps
After you upgrade to SQL Server ...
Update statistics — To help optimize query performance, we recommend that you update statistics on all databases following upgrade. Use the sp_updatestats stored procedure to update statistics in user-defined tables in SQL Server databases.
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