I have the 3.42 gears and overall pretty satisfied. Usually check MPG's on runs up to our camp approx 75 miles from home. 8 miles at average of 40 mph, then 57 miles on the interstate with cruise set at 70, then another 7 miles on back roads around 45-50.
If I'm running with nothing loaded it gets 15 mpg, 20.5, and back to 15 again. About 17-18 average for the trip.
If running loaded: groceries, utility trailer with a John Deere lawn tractor, weed eater, gas, and any tools I might need (2200 lbs towed), and 2 adults it drops 1-1.5 mpg to 16-16.5 for the trip.
Quite happy with this. It's 3 mpg better than the F-150 with the 5.4L and 3.55 gears I traded in.
Not sure if there would be any benefit going to the 3.23 in my case IMHO.