Query Response time

 Hi  All
I have  a query taking around 6 Min on one system and  few seconds on  another similar system.

SELECT   /*+ INDEX_COMBINE(F) */
                     CM_ID,
                         CM_DESC,
                         SUM(SUM_BYTES_DOWN)/1000/1000/1000 SUM_BYTES_DOWN,
                         SUM(SUM_BYTES_UP)/1000/1000/1000   SUM_BYTES_UP
                FROM     CM_HOUR_FACTS F
                WHERE    UP_ID IN 48030822  AND   
                                HOUR_STAMP BETWEEN TO_DATE('2010-02-18 15:00:00', 'YYYY-MM-DD HH24:MI:SS')
                                                                 AND TO_DATE('2010-02-25 15:00:00', 'YYYY-MM-DD HH24:MI:SS')
                GROUP BY CM_ID,
                         CM_DESC
                ORDER BY SUM_BYTES_DOWN DESC,
                         SUM_BYTES_UP   DESC;



Access Paths
--------------------------------------------------------------------------------
  SORT ORDER BY
    HASH GROUP BY