bnx2 udp multicast packet loss and jtter

Hello,

I get some bad packet loss and high jitter on a BCM5709. This is on
kernel 2.6.38-8 - unfortunately using a newer kernel isn't an option
right now.
The bnx2 driver is version v2.0.23b.

I've tried a lot of kenel types such as -lowlatency, -ck and vanilla.
The thread doing the udp output is at realtime priority and the same
thing happens with different applications.

Example of jitter
http://dl.dropbox.com/u/2701213/jitter.png

Is there anything I can do to further diagnose this problem?

Regards,

Kieran Kunhya