Help diagnosing wireless network connection problems

I'm been having some network problems and I'm really not sure to make of any of them. Networking was never my strong point, but I've done everything I'm capable of to try and diagnose and fix this problem.

So I have comcast and use my own router. The last router I had was a netgear and needed replaced because it would restart itself randomly multiple times a day and I'd be without internet for about 2-3 minutes at a time. Instead of trying constantly to fix it I just bought a linksys C1000 to replace it with.

This problem started happening a little over a month ago and it manifests is self differently every time and the symptoms just don't at up in any logical way, before I go out and buy a new router I want to ask you guys. Obviously, I get disconnected for about a minute at a time, but I also have long periods of just EXTREMELY slow internet speeds. I'm talking 100mbps down to less than 1mbps. The odd part comes in when I do a speed test during one of these drops in speed. The speed test says I'm getting all 100mbps of my connection, but the youtube video I'll be watching will need to buffer.

Pages will also load very slowly, but not all of them. Techspot, Youtube, and Outlook all take forever to load during these slow downs, but others will load just fine.

I can't figure out if this is the router or comcast. It problem seems like it is a router problem because of me getting disconnected from my router, but during these slow downs I can still access my router just fine and my internet speed will be displayed correctly. I only have one computer connected to wifi so I can't test other machines.

What do you guys make of this? Also, what are some tests I can run to help diagnose this problem? I'm at wits end about this whole thing. The disconnects seems to have stopped when I changed channels in my router to channel 9, but I'm still having this severe slow down issue.

Also, as a side note, I recently upgraded to xfinity and it came with a new modem. These slowdowns have been occurring on both modems which leads me to believe it is the router. Here is what I've tried doing so far

>upgrading firmware
>changing ethernet cables
>changing modems
>changing wireless cards
>adjusting channels
>using different types of security(WEP, MAC, WPA)
>reinstalling windows
>using different browsers