Data retransmitted via GRPS

Hi all!!, im doing an GRPS aplicattion where i send 512bytes packets to a server. Snuffing with Ethereal i noticed that a lots of packets are retransmitted by my cpu, that usually hapend in TCP IP ehwn the host cant read the acknowledge. In my case, my CPU doesnt seem to be able to read the ack so he sends again the packet. That makes the speed really go down.

Does anyone knows why is this happend to me?. Im using a q2687 Classic.

Thank u for advance.