Ping depends on everything between your computer and the destination, it may not have anything to do with things on your end. Do a traceroute to the destination and try pinging individual hops along the way to find out where things may be breaking down.
Years ago, I had chronic lag issues in WoW. After identifying what addresses belonged to Blizzard servers, it turned out the cause of severe lag was the hand-off between Blizzard and AT&T. It took over a month for Blizzard to get its problematic links to AT&T fixed.