I have had this problem for five or six months. Finally verizon sent me a new router. It did not help. It rebooted several times a day. So a technician came out and installed yet another router, saying the other ones might have been remanufactured and this one is brand new. It rebooted three times in the first hour. So I found this thread, and someone suggested the IGMP feature might be a problem.
http://192.168.1.1/index.cgi?active_page=6059
Above is the hidden page for disabling IGMP.
IGMP Proxy (Enable/Disable):
I simply changed "enabled" to "disabled" and hit the "Apply" button.
I have now been up for 80 hours without a reboot.