There are multiple options.
a) You can set the z-index of the ui-autocomplete div to a high number with the position being absolute, and using important tag.
.ui-autocomplete
{
position:absolute;
z-index:9999 !important
}
b) You can use the Open and close function and set appropriate z-indexes for the ui-slider-handle.
$( "#controlname" ).autocomplete({
...
open: function(event, ui) { $(".ui-slider-handle").css("z-index", -1); },
close: function(event, ui) { $(".ui-slider-handle").css("z-index", 9999); }
...
});
Hope this helps.