Looking to upgrade to 4.1. Currently on 3.1.3 JB (Spirit) baseband 5.12.01 Iphone 3GS. I have created a custom IPSW with pawnage tool. All I should have to do is the restore option in iTunes if I am not mistaken. Is this correct? Is there any issues I should be aware of? Or should I just upgrade to 4.2 through iTunes then do the JB? There are no issues doing the upgrade on a windows computer even though the ISPW was created on a MAC? And the last question if something goes wrong, I should be able to go to DFU mode and do the restore with no problems?