Alright so after doing a bunch of searching, I have come to the idea of swapping to a 02+ WRX ECU and merging the harness. I currently have a 4eat which I plan to keep and was wondering since the 02+ ECU's are able to be tuned with the 4EAT. Would I just need to do a normal harness merge and ECU swap or would I also need to swap the 02+ TCU? The 99+ have a phase 2 trans but have phase 1 electronics so I'm assuming the TCU is different than the phase 2. Can anyone confirm if they are the same/different TCU's?
I'm pretty sure I'd need to swap the harness, ECU and TCU. But I cant seem to find much on the TCU as everyone usually swaps to manual on the 2nd gen.