As said, the '13 and up models have significant changes. '12 and older have the same drivetrain as 3rd Gen trucks down to 07.5. Not a bad thing, but the major chassis upgrades are significant on the newer models. Bigger or stronger frame, brakes, front end components and axles. Plus the better mileage of scr emissions. And you can get a srw truck with the Aisin trans potentially.
Bad part is it seems apples to apples, early 4th gen truck owners seem to ask just as much for them as the 13-14 models.