"resolving host..." wait wait wait and wait some more........

Been getting this 'resolving host' issue for a while now and can't seem to resolve it (pun, maybe).  Cycled through a number of the DNS options including the default Cox options but the problem still persists.  Enter a new URL and it could take 15 to 20 seconds or longer to resolve the site and connect.  The line speed tests fine and usually fast but with some wild variations.  Thing is, I also have a 3Mbps DSL in addition to the cox 150Mbps connection.  The 3Mbps ALWAYS resolves instantly and often provides faster downloads than the 150Mbps connection.  Go figure.  And all that for the privilege of having TV and Internet for $300/mo.