I was a little skeptical about the 3.42 rear end but after about 9000 miles I am happy with it. I tow a 14, 000 lb fifth wheel and on relatively flat ground it will stay in 6th gear. At 1500 rpm I am running 68 mph. And average about 10.5 to 11 mpg. Start bucking a strong head wind or hills and I will lock out 6th gear. If I remember correctly when I am turning about 1700rpm I will be running about 70 mph. With sixth gear locked out . Still get about 10.5 to 11 mpg. Takes a pretty good hill to make it shift from 5th to 4th.
Very happy with the 3.42 and the truck in general.