Don't rely solely on a one-line slogan to make your page rank high.
What you want to achieve is unique content on every page, and make sure each page is rich with text-based content so that people who can't see images or that use screen readers can understand the page.
While the slogan on every page counts as duplicate content, the impact wont be as high if each page has unique text with at least a few hundred words. If however your pages consist of what you described in your question (aka template) along with just one unique image for each page with the same "template" then you'll run into severe duplicate content and thin content problems because search engine robots can't convert images into text it can understand for search engine indexing.
Make sure when you revise your pages, you run them through a site that checks the amount of duplicate content for you. Doing a search on Google should give you some sites.
And just because you might have hit high in search engine results today doesn't mean you will tomorrow. Sign up for Google webmaster tools if you haven't done so to see what keywords users use to access your site from Google. As a bonus, in the HTML improvements section of webmaster tools, Google can indicate if you have duplicate title and meta description tags.