Date Object in WebI too slow

All,

     We are facing an strange issue in BI 4.1 SP3 Production Environment.

We have few reports that have a date object (Created_date) included in the query.

     1. The report takes 3 hours to complete.

     2. The same query run directly against the DB takes 1 minute.

     3. We pointed the same universe in Dev environment to the prod connection and the reports completes in 1 min.

     4. In production I changed the object format to character and the report ran inside a minute.

We are totally confused with what is happening the date format object in the production alone. our DB is oracle and the actual format of the object in the DB is also date.

Any suggestions would be of great help.