performance issue in retrieving data from AD through LDAP

We have IS 6.0.1 with IS_6-0-1_SP2 sitting on 2 win2k servers and they are clustered. We have flow services which are using pub.ldap:search service to retrieve list of attributes for all employees with certain filters on them. Now the issue is we absolutely have no issues connecting to the same LDAPURL from our Dev/QA environment which is in a different subnet than that of the AD. However, our prod systems are in the same subnet and in the same network as well but we get into performance issues while running these data retrieval searches when we try to run the Allemployees listing. We get immediate responses back when we query per employee…

So, it works fine if we query per employee and we get to this issue when we try to retrieve all employees’ data.

Recently they changed the Domain controllers at the network level and since then we have this issue. Not sure what would have caused this. Any help in this regard would be very much appreciated.