Default Connection problem with the upgrade to kitkat

My internet connection is perfect when my ROM is jelly bean. When I upgrade to kitkat it is very slowly. I have just send my phone to the assistance and they install me 4.3 android but I can't reinstall kit kat because the connection doesn't work well (I have already try to reinstall it but nothing) I have always update with ota. You have many advice for me?

Inviato dal mio Nexus 4 utilizzando Tapatalk