Hi ,

You can possibly looks at areas in SQL database

1. If lot reads or updates based on SELECT CONDITION check if the indexe statistics are up to date, if not issue UPDATE STATISTICS on database.

2. Check if the index are not fragmented for indexes having greater than 10K data pages.

3. Is execution plan different than SQL 2005 used for qureies, if yes does step one or two resolve it ?

4. Are you running with compatbility level of older version that is SQL 2005 is 90 or using the new compatibily level in SQL2008 which is 100 , have you tested this ?