Chasing referrals in Active Directory (ie: searching across domains), can be slow.  You can look up the object instead in the GC (Global Catalog) as follows:

Remove any reference to ldap:// when you use ldap_connect, ie: use "serv1.mydom.com" NOT "ldap://serv1.mydom.com"

Connect to port 3268 (not 389, the default)

Set the Base DN for the search to null ie: "" (empty quotes).  

AD will then run the search against the GC which holds a copy of all objects in the Forest.  You can also retrieve a subset of attributes (including group membership, except local groups).

You will still need to follow referals for a full set of attributes.