If you have a Gig connection on your Linux server, your O/S might be robbing you of power. Try this out to start with, if it doesn’t work, reboot and your server will default back to their original settings

sysctl -w net.core.rmem_max=8388608
sysctl -w net.core.wmem_max=8388608
sysctl -w net.core.rmem_default=65536
sysctl -w net.core.wmem_default=65536
sysctl -w net.ipv4.tcp_rmem=’4096 87380 8388608′
sysctl -w net.ipv4.tcp_wmem=’4096 65536 8388608′
sysctl -w net.ipv4.tcp_mem=’8388608 8388608 8388608′
sysctl -w net.ipv4.route.flush=1