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the true way to see your us results is to use a US proxy.
Search for proxy list in google, then set the proxy in your browser, in IE its Tools/Connections then the Lan Settings button.
then if your browser redirects to .co.uk when you do a search, change it too .com and do the search you are wishing to see again.
This is particularly relevant if you have a .com domain on US hosting and want to know what penalty a site maybe incurring in google.co.uk.
I use this method to see where a term will rank before moving to uk hosting for a site that is penialised because of its US hosting or TLD ( penialised in .co.uk).
An example is:
no5 for a term in: google.co.uk
no3 for a term in google.com
no1 for a term in google.com via a US proxy
this is for a .com site with US hosting.
Hope this helps.