The Tranny code is the same, but best bet is to ask a dealer to make sure. Then when you buy one, make sure that they guarantee the compatability.
Again, drawing from what I know, just because it has the same code doesn't mean that it's exactly the same. The New Mits Evo engines have the same 4G63 designation as the old Turbo Eclipses, but the Cams and the Serpentine Belt is on the opposite side (right side of the car as opposed to the left side from years previous). The exhaust manifold is still in the front, so that means that the engine didn't just simply get turned around. Sometimes, minor changes doesn't warrant a complete renaming of a part, but it does make a difference. That's not to say that a 2003 tranny won't work, just a word of caution.