This is primarily a TCP related question, so if there is a more appropriate forum for this question, please point me in the right direction.

I am trying to identify the source of a slowdown for an upload to Amazon S3 from a Windows 2008 server.  Packet captures seem to indicate the problem is with the TCP window size.  When I manually increase the TCP window size on another machine, I am easily able to get maximum bandwidth utilization.  But, for some reason, this 2008 machine won’t increase the window size beyond 64K.

I can’t increase the TCP Window size on the 2008 machine because of the new and “improved” auto tcp tuning.  Is there something else I should be looking for that could be causing the window size to not be scaled any higher?