slow network file access on 2k3 sp1 and sp2 R2 server

Hello,

One of our remote offices began complaining of slow network file access of
Excel files on their file server/DC which was a Win2k3 sp1 R1 server.
Certain Excel files (almost all have links to other Excel files on the same
server) would take 60 seconds to 2-4 minutes to open, before prompting to
update the data w/in the files. Prior to this it would take 15 seconds or
less to open the same files.

We were unable to find anything wrong with the server through the event
viewer, net/dcdiag, etc. After a great deal of pressure from this office we
replaced the server with a newer Win2k3 sp2 R2 server and migrated the data
to the new server. The slow access followed over to the new server. Again,
nothing in the event viewer and all diagnostics come back as normal.

We moved a copy of all the data to the phone server in that office, Win2k3
sp1 (no R2) and the Excel files in question open in 1-2 seconds.

Any ideas on what else to check or tweaks to R2 to improve network file
access?

Thanks in advance!