Are you integrating adsense using JavaScript, i.e. including some kind
of JS script from adsense? If so, are you dropping the script
reference into the <head> or at the bottom of your HTML document? If
it's near the top of your document then it will stall execution/
rendering of the rest of your document until the script tag is loaded
fully from adsense's servers.
If you have a script tag inserted for third party scripts hosted on an
external server then I recommend dropping that script tag right before
your closing </html> brace.