Tow,
They changed ratios in 6th? What was the final ratio in the 'new' O.D. gearing? My records indicate the G56 had these ratios:
6.29/3.48/2.10/1.38/1.00/0.79/5.74R (lower 1st gear; less tall 21% O.D.)
and the NV5600 had:
5.63/3.38/2.04/1.39/1.00/0.73/5.63R (higher 1st gear; taller 27% O.D.)
To the question: gearing all depends on how much load/tow weight you are up to, and
how much torque the engine of your particular year puts out. On the last few years of the Ram, the TQ rating is so high that it will twist at a loaf with taller 3.42:1 gears. Because it can.
On earlier Rams with lessTQ a higher numerical rear end ratio is in order. Then again, my 3.55:1 pigs and 33.1" tires dictate spending a bit more time in 5th,with my tinky 505 #ft, which I think is a good thing as the O.D., 6th gear is smallest of the gears and more likely to fail. As to the pigs, there is a train of thought that a lower numerical pinion (like 3:42:1) is larger with more gear surface than a higher numerical gear and less likely to cause woes down the road.
I think you could learn to drive each choice of gearing over time, massaging the trans to meet the grade or speed.
Just my opinion.
jefe