install 6.1.3 on ipod

i have a 4th gen 64gb ipod i use to play movies in the car. the device i use lockpick gmx550 worked fine with 6.1.3 for the longest time. i recently plugged my ipod into the computer to sync and apparently updated to a newer ios. i thought 6.1.3 was the final release and it would never update? anyways, now it no longer works in the truck and i cannot seem to get back to 6.1.3; i've downloaded the ipsw file and place the ipod in restore mode, browse to the file and it says could not be restored error 3194 or "This device isn't eligible for the requested build". i also googled how to fix that issue and tried to place paths in the hosts file with no luck. please help!