I am trying to conditionally format a list of approximately 12,000 addresses so that entries that are duplicates in two categories are highlighted. I tried using the formula

=AND(COUNTIF($B$2:$B$11,B2)>1,COUNTIF($C$2:$C$11,C2)>1)

The problem with this algorithm is that it returns entries that match others
in both areas regardless of whether the matches are in the same entry. For
example if I have the list:

John Cincinnati
Zach New York
Zach Cincinnati

The last entry will be highlighted although it is not a true duplicate.

In addition, it slows my spreadsheet to a crawl, even when I save and reopen it takes five minutes to load.

Finally, I am unable to edit the format of individual entries, which is necessary for when I go through to check for errors.

Any help would be appreciated.

Thanks,
Zach