Windows XP Pro slow opening files on network after 2003 migration

I have a strange problem I have a 2003 Domain which i just migrated to new hardware. all of the pcs are slow accessing files on the server. Any new XP Pro pcs added to the domain are fine. I have checked the registry for old references to the old server and change or deleted the reference and unjoined the domain renamed the a pc and rejoined the domain. Still the same issue. Any help would be appreciated I really don’t want to reload the pcs.