If you haven’t noticed by now, there is no one thing to point at to say what makes this transmission better now than it was. There are so many co-dependent systems in an automatic transmission that it all needs to be modified with an eye to all the other mods. Nowhere is that more true than in the valvebody. The profile of the valves combines with the stiffness of the springs, which combines with custom maching of the new valvebody to alter line pressures in all different scenarios. Since the fluid pressure inside the trans helps hold gears, alters shift points, and basically does all the "automatic" part, this is key.