Just for your data. I recently traded my 2015 Ram 2500 mega cab for a 2018 Ram 3500 mega cab DRW. Here's my info if it helps.
2015 Ram 2500 Mega Cab 4x4 Laramie - Auto Trans - 3.42 gears
Empty around town - 11-12 mpg
Empty highway - 20-22 mpg (best mileage was 22.5 with my wife driving avg between 60-65 mph... I got 21.5 driving 75-80 mph)
Towing ~7k lb trailer with Jeep Wrangler on it - 14-16 mpg
Towing ~7k lb trailer with Jeep + ~2500 lb popup tandem - 11-12 mpg (from Houston to Marble Falls, TX.. flat to somewhat hilly terrain)
Towing ~14k lb Road Warrior - 9 mpg (from Houston to Mason, TX.. flat to somewhat hilly terrain)
2018 Ram 3500 DRW Mega Cab 4x4 Laramie - Auto Trans - 3.42 gears (not Aisin unfortunately)
Empty around town - 11 mpg
Empty highway - haven't really tested yet, best I've gotten is 17 mpg with mixed highway/city
Towing ~7k lb trailer with Jeep - haven't tested yet
Towing ~14k lb Road Warrior - 9.3 mpg (from Houston to New Braunfels, TX.. flat to slightly hilly terrain)
2015 Ram 2500 Mega Cab 4x4 Laramie - Auto Trans - 3.42 gears
Empty around town - 11-12 mpg
Empty highway - 20-22 mpg (best mileage was 22.5 with my wife driving avg between 60-65 mph... I got 21.5 driving 75-80 mph)
Towing ~7k lb trailer with Jeep Wrangler on it - 14-16 mpg
Towing ~7k lb trailer with Jeep + ~2500 lb popup tandem - 11-12 mpg (from Houston to Marble Falls, TX.. flat to somewhat hilly terrain)
Towing ~14k lb Road Warrior - 9 mpg (from Houston to Mason, TX.. flat to somewhat hilly terrain)
2018 Ram 3500 DRW Mega Cab 4x4 Laramie - Auto Trans - 3.42 gears (not Aisin unfortunately)
Empty around town - 11 mpg
Empty highway - haven't really tested yet, best I've gotten is 17 mpg with mixed highway/city
Towing ~7k lb trailer with Jeep - haven't tested yet
Towing ~14k lb Road Warrior - 9.3 mpg (from Houston to New Braunfels, TX.. flat to slightly hilly terrain)