Why the Tx performance of the Intel 82559 NetCard driver is

We have a question about the Intel 82559 NetCard driver we used now.

While the Intel 82559 NetCard Rx flow increase to 20Mbps, and Tx flow
increase to 8Mbps, we found the number of FIFO Underruns During Tx(by useing
Netinfo -l )increase very quickly. We wonder why the Tx performance of the
Intel 82559 NetCard driver is so bad.

How can we improve the Tx performance of the Intel 82559 NetCard driver?

We also hope somebady can give us the newest Intel 82559 NetCard driver.

Thanks a lot.

Can anyone give me the newest Intel 82559 NetCard driver?