Google "how to edit host file". You'll get plenty of links. Once you know how to,edit it, remove any references to ga.apple,com.
If your host file contains no reference to gs.apple.com, then the only thing I can think of is you have the wrong ipsw file. Double and triple check to make sure you have the right one.
If your host file contains no reference to gs.apple.com, then the only thing I can think of is you have the wrong ipsw file. Double and triple check to make sure you have the right one.