I love the 4.10s in my 3rd gen 6.7 Cummins. While it doesn't get the mileage my 12 valve with 3.55s did, not towing of course, it does me just fine.
On that note when I decided I needed a tow rig I got a Chevy 1500 Z71 that averaged 4mpg towing my jeep, slightly better down hill. I replaced it...