While I know many architectures like ASP.NET MVC have built-in functionality to handle JSON.stringify as the contentType my situation is a little different so maybe this may help someone in the future. I know it would have saved me hours!
Since my http requests are being handled by a CGI API from IBM (AS400 environment) on a different subdomain these requests are cross origin, hence the jsonp. I actually send my ajax via javascript object(s). Here is an example of my ajax POST:
var data = {USER : localProfile,
INSTANCE : "HTHACKNEY",
PAGE : $('select[name="PAGE"]').val(),
TITLE : $("input[name='TITLE']").val(),
HTML : html,
STARTDATE : $("input[name='STARTDATE']").val(),
ENDDATE : $("input[name='ENDDATE']").val(),
ARCHIVE : $("input[name='ARCHIVE']").val(),
ACTIVE : $("input[name='ACTIVE']").val(),
URGENT : $("input[name='URGENT']").val(),
AUTHLST : authStr};
//console.log(data);
$.ajax({
type: "POST",
url: "http://www.domian.com/webservicepgm?callback=?",
data: data,
dataType:'jsonp'
}).
done(function(data){
//handle data.WHATEVER
});