Ive been looking at gamerscore modding. I have wrote out this tutorial for you all.
You DONT need a data transfer cable to do this, Just a normal usb.
Ok now with the tutorial..
First, Plug USB into Xbox 360
Go to System Settings -> Memory -> Configure -> USB Storage Device -> Configure Now
Now you need to copy your profile to USB
Plug USB Into Computer
You will need to download Modio, USB Xplorer & Profile Editor (See Below for links)
Now once you have all the files downloaded, Open up USB Xplorer
Load your file into the program.
Go to Content and find your GT
Go thru all the files untill you get to the last one.
Extract that last file to your desktop or wherever
Now, Open up profile editor
Click OPEN and find the file you extracted
All your games will be on the side of the program.
Choose your game you want to unlock all achievements with.
Now this step is important, Where it says [ Locked, Offline , Online ] Make sure you press OFFLINE.
You can now press unlock all
Once your done unlocking all acheivements, Press the Xbox Logo and press save.
You can now close Profile Editor.
Now, Open up Modio.
When it has finished opening, Open your profile file.
Press Rehash & Resign. DONT PRESS ANYTHING ELSE!
Once it says Rehashed & Resigned on the bottom left, You can exit out.
Now open up USB Xplorer again and go to the same file where you origionally got this file from
Now, You press Inject and inject the modded file.
Once it has injected, You need to DELETE the origional file.
Once you have done that, Youu can just close it off, Plug in your USB and sign in on that GT.