http://forum.ppcgeeks.com/showthread.php?t=24511
Follow that guide. I did and now I have a USCC with GPS.
It gets kind of bland in the middle when the Hard Spl gives instructions to dissconnect the phone and reconnect it though.
Just follow everything as stated and you will be on your way.
And there is no going back on USCC. Since it doesn't seem like a current ROM has been leaked yet or an official upgrade is released which it probably won't happen either.