Change your DNS in the router and check if it fixes it.
Either OpenDNS or Google DNS.
208.67.222.222 and 208.67.220.220 (OpenDNS)
8.8.8.8 and 8.8.4.4 (Google DNS)
Typically, ISP's DNS servers are the biggest bottleneck. I would recommend using a 3rd party DNS service always.