TraderDan, that is still not the right file ...

If you edit the file, you will see it contains on line 3:
* USPS Module for Zen Cart v1.3.x, revised May 12, 2008 for new USPS rates effective May 12, 2008
And that the ID on line 9 is:
* @version $Id: usps.php 8516 2008-05-13 01:56:07Z drbyte $
Get the USPS May 12 2008 download and load it to the directory:
/includes/modules/shipping

If you then search it and get the wrong date, delete the file on the server ... and then load it ...