I’ve been noticing a lot of slowness that I’ve traced to DNS issues lately, typically with the caching DNS in routers. It happened to me, and it happened to my mom. We have different routers from different manufacturers, and they probably even use different embedded operating systems. Hers almost assuredly runs Linux; I have an oddball one that runs FreeBSD.
But the caching nameservers aren’t working well lately. I haven’t investigated why just yet. The solution I found was to hard-code the DNS settings on all my computers rather than letting them pull it from DHCP (my oddball router won’t let me specify external DNSs to use–lovely). Be sure to pick the best ones for your network.
Making that simple change fixed my mom’s dog-slow computer, and fixed my unreliable one.