Really Bad Lag Spikes in Games

When I'm playing any online game, every few minutes, I get a really, really bad lag spike. I don't mean a frame rate drop, and I don't mean a generic rise in latency. The game state totally freezes up and undoes my actions for the past few seconds. This effect usually comes in pairs (lag spike, couple seconds pass, then another lag spike, followed by a number of minutes of normal connectivity). This is not an issue with any specific game (happens in everything from League of Legends to TF2). I've tried the following:

• Updating Windows

• Updating my network device driver

• Scanning for malware

• Turning off programs I notice running, including Steam and Microsoft Security Essentials

• Unplugging my LAN cord, waiting a few minutes, and plugging it back in

• Deleting my saved networks

• ipconfig release and renew

• Running CCleaner

• Disabling my wireless network device (it's been off the whole time, just to be clear)

• Disabling my wired network device, waiting a few minutes, and re-enabling it

• Rebooting, obviously

This problem seemed to start right after going back to my university, so the problem might be network-specific. I should also point out that the university requires I use Cisco NAC to use the internet, which could also be the cause of the problems, but they had the same requirement for the previous two years and there were no issues. When I contacted campus tech support, no one had heard of the problem happening to anyone else.

I'm running Windows Vista SP2. My network adapter is Marvell Yukon 88E8055 PCS-E Gigabit Ethernet Controller on driver version 11.30.1.3 (9/15/2010).