Bee,  I had a similar problem and resolved it by sorting the lookup i.e in
your example, the zip codes.

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     Vlookup gives wrong answer

     Niek Otten, April 1 2006

     Frequent causes:

     1. Some cells look like numbers, but are actually text. You can check with the ISTEXT function.
     Check both the search arguments and the lookup table.
      Formatting as numbers afterwards doesn't help.
     Remedy:
     Format an empty cell as Number. Enter the number 1. Edit>Copy. Select your "numbers". Edit>Paste Special, check Multiply.

     2. The data is not sorted ascending and the 4th argument of the VLOOKUP is TRUE or is omitted.

     3. There are spaces or other invisible characters in either the search arguments or the lookup table.
     This often happens when you import data from other applications.
      Use the LEN() function to see how many characters there really are in the cell and compare that with what you see.
     Use the TRIM function to remove all spaces except single spaces between words.
     Use the CLEAN function to remove all nonprintable characters. HTML characters can be removed with a macro by David
McRitchie,
     which can be downloaded here: http://www.mvps.org/dmcritchie/excel/join.htm#trimall

     4. The formula was copied from somewhere else, but the addresses of the lookup table were not absolute so have changed in
the Paste process
     and now point to the wrong range.
     Use absolute addresses for the lookup table, like $A$1:$B$20 instead of relative addresses like A1:B20.
     When editing or entering a formula, use the F4 key to toggle between several forms of relative addresses and absolute ones
     (normally only for the table, not for the search argument, but this depends on your specific problem).
     The first hit of F4 changes the default relative address to an absolute one. That is usually what you need.
     Even better: use a Defined Name for the table instead of cell addresses; Insert>Name>Define.

     5. The table was extended after its initial use, but the definition of the table in the VLOOKUP or in the Defined Name was
not adjusted accordingly.
     To prevent this from happening: always use explicit bottom and top rows (with dummy error values if necessary)
     and insert new rows or cells between those two.
     Then the definition of the range or the Defined Name will adjust automatically.
     Users of Excel 2003 and higher may profit from the List feature in the Data menu to maintain tables.
     =========================================================

     --
     Kind regards,

     Niek Otten
     Microsoft MVP - Excel