I am having a similar problem on one of my sites.  I recently moved the site from a dedicated server hosted at one provider to a new dedicated server hosted at Rackspace.  That seems to be about the time that the slow load issue started.  Every page of the site loads slowly (15-20 second delay).  I've noticed that pages come up pretty quickly in Firefox after they are initially loaded.  I assume this is some type of browser caching.  Chrome, IE and Safari load every page slowly every time though.  

To further complicate the issue, I have 3 other sites running the same version of DNN on this server, connecting to the same backend SQL server, and they are performing well (no page delays.)  I can't find any differences in IIS or the DNN Host settings between the problem site and these others.

I have followed the suggestions on Mitchel Sellers' site and did notice considerable improvement in the other 3 sites after applying these changes.  My problem site is unfortunately still a problem though.  Frustrated....

 FYI... found the resolution to my problem was Sitetrack module.  Sitetrack requires a "hidden" module to be present on all pages of the site and there is a reference to a webservice in the module settings.  When I moved the site from one server to another, I did not add the DNS entries for this portal alias, so the module was trying to hit a webservice that no longer existed... on every page of the site!

This one really put me though the ringer, but I'm glad to have it resolved.  I realize this does not solve the problem of the original poster, but I thought the problem was related initially and now I am just providing this info in hopes that it will help someone out someday.