Stephen Hemminger wrote:

That motherboard has dual lan, are you using both of them?
I don't have that chip version, so hard to tell if it is using dual port 
with a single chip
or not.  There is a hack for the dual port PCI-X version already in the 
driver,
that turns off receive checksums if both ports are in use. Please try 
turning off
receive checksums with ethtool and see if that helps.

I'm only using one port.  The second port is disabled in the BIOS.  The 
problem still occurs with receive checksums off.