I wonder if you could help please.....

I have a website with around 11,000 URLs. I have submitted a sitemap to google which clearly indicates priority urls. However since uploading my sitemap (1 week ago) i am still finding urls being returned from google searches that i don't want returning. Google is returning pages that are lower in priority on my sitemap than the pages that i actually want returning. On further investigation the page that is being returned has been cached more recently, what does this mean? Why is google caching a page of lower priority ahead of a page with a higher priority?

Any help would be appreciated.