I would move the result header changes into the same success callback like this:
// Set sessionStorage paramater on click
$('#findLocations').click(function() {
$.ajax({
type: "GET",
dataType: "html",
url: "/search/georesults.html",
success: function(closestRep) {
$('.result').html(closestRep);
$('.resultHeader').html('Stores nearest <div class="zip">' + userZip + '</div>');
} // end success
}); // end ajax
sessionStorage.UseIP = "Yes"
});
// Check for UseIP and display nearest locations if set
if ( sessionStorage.UseIP == "Yes" ){
$.ajax({
type: "GET",
dataType: "html",
url: "/search/georesults.html",
success: function(closestLocation) {
$('.result').html(closestLocation);
$('.resultHeader').html('Stores nearest <div class="zip">' + userZip + '</div>');
} // end success
}); // end ajax
}
Note, it might be worth-while to add a separate function for changing both at the same time. You can use that as your callback and avoid 2 sections of code to maintain.