David,
Remember that while Google (and your shoppers) like 'responsive' , at the moment Google is just asking for your store to be mobile-friendly if you want to show up in mobile search results. There are quicker, cheaper ways to be mobile-friendly so that may be having an impact.
Also, you say 'my page is still ranking the same' but I wonder what measurement you're monitoring. Have you tried picking up a narrow device like a smartphone and doing a search for one of your key-terms? (Don't search on your domain name, or your company name - if you're the ONLY result then Google is likely to return your pages regardless of algorithm.
