[CentOS] Ethernet poor performance

I am attempting to build an IPv4/IPv6 router.  I have put a 2nd ethernet 
card in a box.

I have one Ethernet card attached to my network and the other to a 
switch with nothing else there just so the link comes up for testing.

When I have the built-in Ethernet attached to my network, I get pings 
around 60ms.  The other card, btw, does not have any IP addresses configed.


When I switch the cards around, the addon card attached to my network, I 
get pings that alternate with one being ~1488ms and the next 488ms!  
This is regular.

This is the 2nd card I have tried.  The 1st one was getting ping times 
of 1900ms/900ms.

I have played around with the IRQ for the 2nd card.  The 1st card I 
tried I was limited to 9,10, or 11.  The card I am using now allows 3, 
4, or 7 (btw, I have disabled serial and parallel ports).

Any Idea where I should look to fix this?