Download Redsn0w 0.9.14b1. MuscleNerd has confirmed the latest release of the iPhone Dev team's official jailbreak tool which is Redsn0w 0.9.14b1 via his tweet.
Redsn0w 0.9.14b1 will make a possible downgrade for iPhone 3GS on 06:15:00 baseband.
Once the tool download, you can continue to downgrade to 05.13.04 from 06:15:00 baseband in order to fix GPS issue.
Download Redsn0w now based on your existing operating systems:
And if you want to know the guide to downgrade iOS 6 beta 1 to iOS 5.1.1.