Try removing all the web parts and load test and slowly add back one by one. Maybe you can identify a particular webpart that is causing the issue.
The two tools you probably want to use are Debug Diagnostic Too and Fiddler, however I am not an expert on either one.
http://www.microsoft.com/downloads/details.aspx?familyid=28bd5941-c458-46f1-b24d-f60151d875a3&displaylang=enhttp://www.fiddler2.com/fiddler2/Otherwise you can always contact MS Support. I'm sure they can help track down the issue quick.