I tried downgrading an iPhone 4, using Redsn0w, Sn0wbreeze, SHSH methods, stitching, tinyUmbrella. Nothing worked. Redsn0w would get stuck on "Waiting for Device" and the iPhone just stayed in DFU with nothing happening. Sn0wbreeze, using a stitch method and iTunes restore would start, the Sn0wbreeze loading logo and bar would show as if it's about start loading the OS, but then nothing would happened, did not even load a bit, the phone would restart into the "connect to iTunes mode" and that's it. Tried 5.1.1 with Redsn0w and it worked from the very first try. Is there something special about iOS 6 that needs to be done?