Why AutoCompleteExtender is too slow in IE but works fine in Google Chrome

I just upgraded my app from .net 4.0 into 4.5, and installed new version of ajax control toolkit via below link. My current VS is PRO 2012.

http://ajaxcontroltoolkit.codeplex.com/downloads/get/608572

Before it prompted the timeout exception with defult value of AsyncPostBackTimeout, so I changed the default value into 360000.

PS. Error: Sys.WebForms.PageRequestManagerTimeoutException: The server request timed out.

<cc1:ToolkitScriptManager ID="ScriptManager1" runat="server" AsyncPostBackTimeout ="360000">
</cc1:ToolkitScriptManager>

It can let autocomplete loaded data, but it's too slow in IE (9/10). I tested it in Google Chrome, and running perfect.

So I think the key of this issue is loading data of autocomplete looks like slow than normal speed in IE. 

Is there anyone could give me ideas how to fix it? Or how to improve perfomance of autoCompleteExtender.