windows 8.1/IE11 Proxy.pac

We are using a proxy.pac in my compagny, and IE is set to use this :

http://proxyhost.mycompagny.local/proxy.pac

I was working fine on Windows 8 with IE 10 (and also on Window 7 , Windows XP ...)

Since I upgraded to Windows 8.1 , IE 11 take about 30s to load. Let me explain:

I start my computer, then I start IE and it does nothing, it doesn't load or show the URL of my home webpage after 30s it's work

and every time I close to Ie and come after while to opened it take the same time to load

This is very weird.

Thanks in advance for your help