My guess is that you need to report the change to all of the sites that had links to your old site. Even though Google's ranking methods are closely held secrets, I have always found that people accessing your site from another, have a big impact on your ranking.
Don't know if you can still do it, but you should try the search to find out just who has linked to your old site.
The query link:siteURL shows you pages that point to that URL.
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