You have been lucky very lucky. Wireless is great so long as everything you do have some type of buffering working with it. Your fix is easy but the results will be varried.
Run a wire from your router for gaming. I say never play at this level unless your wired.
Reboot the router and modem leave it unpluged for 5 minutes. Try that out.
Reload the wireless driver for your system. If you up graded win 7 might not have the latest.There are 2 ways to run wireless for your system. Via windows or the manufatures system. I think windows is the choice here, But someone please correct me if I remember this one wrong.
If none of that works your router might be going out the door or you erthernet on your MB . You can by add on ethernet cards cheap just check to see it you have a slot for one on your mb and remember to turn off the mb etherbet via the bios.