Quote Originally Posted by 1963SS View Post
I can't speak about the 4T65 transmission but on the 4L60's a Transgo and a tune are usually a bad idea. Since the Transgo kit tends to raise the line pressure so does an ECM change. Too much of a good thing is not necessarily a good thing.
Shift kits on 4t65e's actually lower trans pressure as far as I know. Shifts get faster due to the springs being stiffer (not directly related to pressure, just modifies the cushion on the apply lines), and the computer recognizes it's shifting faster and will then adapt using pressure.