|You could test to see if it's your modem or your router by plugging the modem directly into the wired network interface on your computer. If it runs fine for a day or two, then your router is likely the problem.|
To test the router I would start by recycling the power on it. Unplug it, count to ten slowly and plug it back in. If everything works fine after that, leave it alone.
If it doesn't work correctly, the next thing to do is ensure you have the most up-to-date version of the firmware installed. If you already do, or updating it doesn't help, then next thing you can try is resetting the router to factory defaults and then reconfigure it.
If none of the above troubleshooting steps on the router work, and you already know the modem is working fine, then it's likely your router is in need of replacing.