I've seen numerous faked screen shots of Golden Sun 3 for DS and Wii, but I haven't heard any word of a real GS3.
I sure hope there is going to be one, tho... Golden Sun is my favorite game of all time.
If you mean 3.71 M33-1 to 3.71 M33-4, then yes. If you are on 3.51 M33-1 or 3.52 M33-1, then you need to upgrade to 3.71 M33-1 before you install 3.71 M33-4