My adsense reports 12,000 monthly pageviews and my analytics reports 15,000 monthly pageviews. How can I act upon this difference and use adsense to fully monetize all the pageviews? Is there some way to see which pages are not with adsense on my site?
Google have answered this question for you: https://support.google.com/adsense/answer/6090783?hl=en-GB
Might not exactly pinpoint the issue, but it really could be a whole lot of reasons. For one, are you absolutely certain that each and every pageview on your site is generating an ad impression?