DNS-like connection issue

We are a small office, connecting via Netgear FVS124G firewall to 2 T1 lines. It may be my imagination, but it seems like it can take 5 to 10 seconds to make a connection to a site. The ISP did find an issue with the timing of the 2 lines to each other, but the problem persists. I have switched to a different DNS, and it seems better, but still pokey. Bandwidth tests show that I'm getting the 3mb pipeline we are paying for, but the lag is annoying. Is there a more scientific test to verify if I have a firewall/router issue on my end?

Things to try (Sorry if you've already tried some of them):
1. Disable one of the T1 links and see if the delay persists.
2. Have you tried using OpenDNS. I had serious problems with my ISP's DNS (BT) with sporadic loading times, etc and the switch resolved the problem.

I'm sure there'll be lots of other suggestions ...

To check/eliminate DNS do an nslookup for some site to obtain the ip address, then try to access the site using the ip address alone rather than the name. This should be a straight access - no lookups to slow it down. Try several tests with several sites and the results should indicate whether or not it is the name resolution that is slowing you down

Duh-Oh! I forgot to change the DNS settings in my Airport.

To prevent something like this happening again in future, if you insist on using static DNS settings instead of dynamically assigned ones in your Airport, it may be better to use something like OpenDNS which will work irrespective of changes in ISP.