5.3L was definitely the sweet spot, and outperformed both the 4.8L and the 6.0L from a power or cost per displacement perspective.
The marketing and planning teams kind of blew it on that one. They wanted to induce most people to get the 4.8L, as lower cost and better fuel economy (to help with corporate fuel economy standards).
What they failed to realize is that most truck buyers want the biggest engine they can get, regardless.