Hello.
It could be a problem with your modem / router, or it could be a problem with your cable connection - or with a wireless network inside your own home. Often when we hear these problems, the problem originates with a wireless network. If you're using wireless, try using hard-wire and see if that solves your problem.
If you're already hard-wired, then run PingPlotter and look for the high latency point. We have quite a few techniques on this tied into our VoIP troubleshooting guide (VoIP and gaming have a lot of similarities):
http://www.pingplotter.com/manual/standard/voiptroubleshooting.htmlFeel free to post a picture here, or send some sample data to our support team to get some more specific guidance.