Switching hosting should not effect ranking, get the site up and running on the new host test everything you can THEN change the DNS; after all of the traffic is showing up at your new site. close the old site.
Check the new site out on spam lists after you have your site on the new host (before you switch hosts, see if you can find out other sites on your server and check out that they are not banned by google.
"Check the new site out on spam lists after you have your site on the new host (before you switch hosts, see if you can find out other sites on your server and check out that they are not banned by google. "
But would a spam list matter if a site is on a dedicated IP address?
