we tow 7000 lb with a 2017 ram 1500, hemi, 8 speed, standard rear axle rather than the 3.92
with the 8 speed, the 3.92 is not needed imho. then we get better mileage when not towing as well. "off the line" performance is still plenty when towing and with the 8 speed the truck has plenty of ratios for highway speeds, one downshift at highway speeds is an rpm boost of 500 rpm, plenty for most hills, another downshift is another 500 rpm
our mileage is around 9.5- 10 L/100km not towing and 22-24 L/100km towing at highway speeds, very respectable as far as we're concerned
ours has the towing package but NOT the air suspension, I wouldn't go for the air suspension, we have plenty of payload leftover anyway