Slow query after upgrade

Last night I upgraded our database instance from 9 to 10.1.0.3   I have a series of reports in report builder that use the same basic sql statement.  The reports in 9i ran in a matter of seconds and since the upgrade the same reports are taking over 20 minutes to run.  I have isolated the part of the query causing a problem.  It is shown below.

 and action2.actn_dt = (SELECT MAX(a5.actn_dt)
                                               FROM cat.action a5
                                              WHERE a5.clm_no = action2.clm_no
                                                                 and a5.actn_typ_cd= 'AS'
                                                                 and a5.actn_dtl_cd in ('AJ', 'GD', 'CW', 'TB', 'MT', 'MP', 'BT', 'CA', 'MV','Z9', 'DY','MS')