What is the weak link for Chevy max tow ratings?

I've read that the limiting factor is the transmission, but as mentioned it probably also has a lot to do with the fact that GM doesn't seem interesting in the "mine is bigger" game Ram and Ford seem to be playing.

For most of us it's academic, and in the tests I've seen the Duramax holds its own just fine against the other two diesels with a comparable load. From a performance standpoint you really can't fault any of the current diesels.