x200 WiFi acting up

I've got an x200 with the Intel 5300 a/g/n card inside.

When I first got the machine, everything seemed to work great. However, now that I've had it a few weeks (and done numerous windows and lenovo updates), my wireless has tanked. I can only seem to get 18-24Mbs while connected, and it's really really slow (I'm currently on ethernet through the ultrabase)

I have verizon FiOS and their actiontec MI424-WR modem/router; the laptop is physically sitting next to it, though I have the same problems when I'm out and about the house. The router's firmware is up to date. I've manually updated the 5300 card drivers from the intel website, I've manually updated the ThinkVantage "access connections" software, as well as removed it entirely (neither worked). I should note I'm using WPA2-Personal on the router (verizon has WEP as default), which shouldn't be a problem but I've read in a few places it might be. I have 3 other laptops connected to the same router (hp zd8000,dell d630, and sager np5790), and they all seem to connect fine, which supports that it's a problem with my x200. I've tried manually setting the card to wireless-g only and it changed nothing.

It worked great before, though, so I'm not sure what I may have done to screw it up. I could do a system restore back to 10/18 if I have to but I really would rather not, since I've installed/configured a lot since then. I might just reformat too, since I eventually want to put a linux partition on here, and there's no time like the present! Still, this problem is bugging me and I can't figure it out.

Any ideas?