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If it was only 2 days, quickly fix the sitemap and re submit it. I do not think Google will punish your sites rankings that quickly. I would also perform a indepth search of links to the new site and see if maybe the site had some bad links and were going to get hit with a penalty for that. You can also view this post for the 301 redirect http://www.seomoz.org/q/can-penalties-be-passed-via-301-redirects

I've never seen anything like that.  I don't think they punish or think its some kind of black hat shenanigans. More likely, loss of traffic may have to do with 301 redirect ?