The auto trans are the same between them, but if I were to replace an SRT6 trans, I would be looking for one from a Mercedes V8 car of the same era, especially one with the supercharged V8. The gear ratios are all the same, but the V8 trans is much stronger, and some of the AMG models feature better shift solenoids, too. Also, they may actually be more common where you are than a SRT6 trans.