CS:Source Lag question

I have been playing CS:Source for over a year now with no problems, i was getting great frame rates, no/little lag, etc.

After an update a few weeks ago, I noticed that my game was lagging out a lot, sometimes for two or three seconds at a time. This seems to happen randomly. During this lag my framerates and latency stayed pretty constant. I did notice that my ping jumped in correspondence to the lag (viewed using the net_graph 3 command), but it does this on every server that I try.

I emailed valve, and they just told me to make sure that I minimize background activities. I have changed nothing on my system in quite a while, so a hardware issue is out. I have uninstalled Source and Steam and then reinstalled, but to no avail. Any idea what could be causing this lag?

My specs:
Overclocked Athlon64 3200+
1 GB corsair
Overclocked 6800gs (513,1131)
Abit AN8 Ultra MB
Dsl 3 Mb/S connection
etc.