I just picked up a real clean 03 LS with a rebuilt trans. I have a rebuilt 3.8... I know the pcm and harness would need to be taken from the other car. But the 4t65e trans is identical in the LS and SS (non supercharged), right? Oh, and would I need to change the axles?

 

The 4t65e between the 3400 and 3800 I believe are geared differently. You would need to confirm that if you are sticking with the 3400 trans. No need to mess with the axles unless you swap to a 4t65e HD.

You would need the PCM from the 3800 and should have the VIN updated. You are also going to need various wiring harnesses and sensors from thew 3800.