Please try this to disable “Large Send Offload” :
1. Open an elevated command prompt and press Enter:
netsh int ip set global taskoffload=disabled
2. Disable and re-enable the network interface.
3. Run the following command in an elevated command prompt to confirm the command above is successful:
netsh int ip show offload
Read this Windows reference guide: http://www.windowsreference.com/windows-vista/slow-network-copy-and-connection-drops-in-windows-7/