Hmmm.

It could definitely be a router / border device on your end of things. If you've eliminated everything at your end of things (which I can't tell for sure, based on the fact that you're having non-trivial wireless connectivity issues and one of your computers works fine), then you're going to need to get your ISP to help you troubleshoot.

It still sounds, though, like your problem is local - since one of your computers is fine and the other is not.

I don't necessarily think there's any problem with the DNS lookups showing CenturyLink.

Since you have two computers at your problem location, try pinging from one computer to the other one. If that shows packet loss, then you can say with quite a bit of certainty that your problem is local - either in a cable, the local router, or with a computer itself.