you are auto if I read right. The auto compared to the 4 speed auto. Nag1 is the nicest part of the "new" stuff. its no 6L but I like the closer ratio 1 to2nd of it. First gear in the auto compared to your 08 auto would be like gearing down a step. 4:1 is like 5:13. One reason it gets the 3:73 it can turn em. OD is only 5th not to high, much better. the reason a auto on 35"s can light the tires up stock 4:1o's without hardly trying. Rubi is worth it more today then before, don't forget the transfer box too is better and lower. do not over rev a rubi in low, the planetary will howl and cook. First now in low on a Rubi Auto in low is like an 08 with a Rubi crawler in a Rubi. its pretty bada$$ for stock. It so low that in low it will not start out 1st it starts out in 2nd in low unless you tap shift to low1st is a manual gear, great for crawling hard stuff.
If this trans was behind a 3.8 no one would have complained about power. It can handle more torque than the manuals at 427 foot pounds stock. They can be built too, don't ask how much its all AMG parts.
The motor well I am on the fence, its had 1 head in 20k. Nice they fix them no issues but still.