Doing more research.It looks like the 2015-2017 is also a larger truck. Longer, taller, wider. I noticed right away that the camper doesn't overhang the cab as much. The truck overall length and wheelbase is about 15 inches longer.
The tow rating is double, and the cargo rating is bigger as well by over 1,000 pounds. GVWR is 1800 pounds more than my 2004.
Putting an additional 300lb/ft of TQ to the pavement probably takes heavier components. The auto trans by itself is about 150 pounds heavier than the 48re as are the axles and most likely the rest of the drivetrain.
There is a noticeable difference in how the truck feels with the same camper in terms of steering input to trucks reaction, stability, sway, braking.
All of this, plus emissions, and lower rear end gear means I should expect less fuel economy. I haven't hand calced a tank yet but going by the notoriously inaccurate dash readout it looks like about 12mpg with the TC on which would be about 3 mpg less than the 04.