Ako si na ASDL-u, onda ti je MTU prevelik.
Btw, ostavi Receive Window Auto-Tuning level na "Normal".
Meni je na W7 (uz MTU=1492) ovako postavljeno:
TCP Global Parameters
----------------------------------------------
Receive-Side Scaling State : enabled
Chimney Offload State : enabled
NetDMA State : enabled
Direct Cache Acess (DCA) : enabled
Receive Window Auto-Tuning Level : normal
Add-On Congestion Control Provider : ctcp
ECN Capability : disabled
RFC 1323 Timestamps : disabled