The 6 speed is a really good transmission, and u know how good the 6.0 already is. The new 6.6 is even better. The engine is the LT1series now and are better then the LS... hard to say that since I’m a die hard LS guy... but if you look up the difference then you will see how much more improved this engine is. Stock, you can easily add more HP and Tq, more so then on the 6.0. It’s all based on the internals and block design. Heads flow better, much better cooling, oil squirters in specific locations such as under the piston, direct fuel injection... the list goes on. I still love my 09 6.0 with 6 speeds though. I like the idea of the 10 speed... I think close ratios are better. It all depends on what you are willing to pay for. Regardless it will be a great truck I’m sure...