talk to your ISP, its probably their fault.

also check your pings to the servers you play on

I'm assuming it's not really a connectivity issue as it is a latency issue (higher ping times), correct?

Have you tried rebooting both your router and/or cable modem (both preferabbly)?

Sometimes they'll get stuck until you reboot (usually happens on routers after a lot of downloading/multiple connections (such as torrents)).

It could also be the server on the other end is having issues? Have you tried any other (more local) servers if your game has an option for that?

Client lease time will only prevent your computer from obtaining a different IP address from your router as quickly (holds on to its address for a longer period). It shouldn't affect your latency.

Edit:
Interesting... sounds kind of like your ISP is resetting the connection for that kind of traffic (similar to the traffic shaping they do with Torrents). Have you contacted your ISP about this?

Also, does your router shape traffic at all? Perhaps your router is set to give higher priority to web traffic as opposed to CS traffic, but this is very unlikely.

Virus/Spyware? Do you check your system for those regularly? (sorry for assuming you're newb or anything... just want to make sure all of our bases are covered).

Edit 2:
Also, in CS, do you get the connection problem message in the corner, or does it kick you out of the game compeletely?

If the latter, it could be a video card driver issue (or some kind of heat issue).

Also, far fetched, but it could be the RAM. Can you take out the ram you added and see how well it works without the new stuff (could be bad ram)? But again, you'd probably notice it would crash the game entirely, and not just give you the 'connection problem' message in CS.