Persistent and systemic Windows 2008 networking failures (DFSR, RPC)

Recently upgraded a Windows 2003 Enterprise R2 SP2 x64 domain controller
(dual quadcore Xeon 3 GHz, 8 GB RAM) to Windows 2008 Enterprise. Since that
time, my clients have had difficulty accessing active directory info, file
shares. This machine is the PDC and RID master as well as a DFS file
server. It's performance is slower by about 20% since the upgrade, and has
persistent connection failure to all machines, especially existing Windows
2003 member servers (32 bit). In particular IPSec, LDAP and RPC (1726 and
1753 errors) connectivity seem to be very problematic at best between 2008
x64 and other clients. 2003 ran much faster and cleaner.

Curious to see if others have had problems in mixed 2003/2008 environments.
From my perspective Windows 2008 64 bit is a poor performer.

Thanks in advance!

Edward Ray
CISM, CISSP, GCIA, GCIH, MCSE+Security, PE
NetSec Consulting