jQuery UI Autocomplete Combobox Very Slow With Large Select Lists

I'm using a modified version of the jQuery UI Autocomplete Combobox, as seen here: http://jqueryui.com/demos/autocomplete/#combobox

What does ExtJS ComboBox triggerAction: "all” really do?

I tried to create a simple ComboBox:

var combo1 = new Ext.form.ComboBox({

  store: [1,2,3],

  renderTo: document.body

});