Has anyone run into an issue with the new MS "enhanced" TCP/IP stack?

Essentially what happened was that over the weekend I upgraded all of my Win2k3 DC's to SP2. Come Monday, myself and two other co-workers (the only ones currently running Vista) noticed that any and all network traffic from our hosts to the DC's was painfully slow!

Remote Desktop was the first thing noticed. Followed by file transfers and even network logins. XP systems did not see this or any issues and all the logs were clean. Even dcdiag /v /e reported nothing out of the ordinary.

What sent me over the edge was the fact that my 'LOGONSERVER' variable was set to a DC located in a different AD site! My system knew the site/subnet it belonged to and was supposed to look for DC's in. Instead it decided to look past the 3 local (and online) ones for the remote DC!

After some digging I found out about Vista's TCP/IP Receive window auto-tuning, which supposedly can dynamically adjust the send/receive windows to up to 16mb based on network conditions.

In any case shutting this down immediately fixed the issue for me:

netsh interface tcp set global autotuninglevel=disabled

Was this "enhanced" stack part of SP2 for Server 2003? I haven't been able to verify this. If not, why did the problem only manifest itself on the Vista systems after the DC upgrades?