2014 dodge diesels

I have been looking at these and I have to ask, why are the new trucks coming out with such high gear ratios? something like 3:42's or the likes. is it for gas mileage or is it because of all the torque the engine has? I don't know how they can tow a 35 ft TT but then I stop and think of the semi's on the road, they also have some high gear ratios.

old guy, don't let the higher gears scare you off, I have the 3:42s in my Ram, pulled the old big heavy brick TT I had very well, it now pulls the fiver with ease... only difference between my 05 with 3:73 vs the 2013 with 3:42 is a little slower off the lights... but then I can now get to campsite with beer and Rum stirred but not shaken. The 3:42s did as well as the 3:73s in the Canadian Rockies.