it takes up to two minutes for each user to logon to the intranet if their cookie has expired. When I look in the dnn event log I see that user is stuck in a loop while logging in giving over 50 login success entries every 1-2 seconds until finally showing the home page. This causes the w3wp.exe on the server to sky rocket in cpu usage. any ideas?

commenting out <add name="Authentication" type="Dotnetnuke.Authentication.ActiveDirectory.HttpModules.AuthenticationModule, DotNetNuke.Authentication.ActiveDirectory" /> seemed to fix the problem. even though the site is listed in my internet options\security as Local Intranet.

Commenting out the Authentication line in your web.config like you did stops the auto-authentication process.