One reason for having an unexplained high ping may be that the Ethernet cable in the back of the router is loose.
Please make sure that the cables are plugged all of the way into the back of the router. This should resolve any unexplained high pings.
If this doesn't fix the issue, please follow the steps here.
Certain modems have a bug which causes this issue. Please see this thread that discusses the solution.
If this doesn't help, then please make a post in the forums including all the necessary information, that way we can help you faster.