Got fast cable and used to work fine but lately it will slow and some pages will not even come up. If I run a net fix utility it again becomes fast but a few hours later it slows to a crawl again.
You could test it by changing it in your IPv4 network adapter properties on the PC first But yea if it's slowing down rather than just not loading pages that doesn't sound like a DNS problem Rebooted the router? Is it running the latest firmware?
Not sure it is the router because that also is hooked to my smart tv and it has good fast connection even when pc does not. Must be in the pc somewhere. When it gets slow and pages refuse to load fast or at all I use this program to fix it but it is only temporary and will slow down again after some hours of use. http://www.majorgeeks.com/files/details/complete_internet_repair.html
It was my graphic cards. I changed out my three 980's for one 1080 and now net loads fast and works great.
Actually that did not fix it. It helped at first but then it started the slow down again. I am still looking for an answer.