Fiat probably wants to sell the 3.73's to get a little better fuel mileage, keeping the RPM's down.... With 800# or torque on the new 6.7's, a 3.73 gear with the six speed auto will work just fine... That 3.73 is the only gear that's ever been available in the GM Duramax 2500/3500 trucks and they seem to pull pretty good. Gonzo will be along shortly, he can tell you what works for him.

How much more can you haul/pull with the 4.10 over the 3.73??

The new Fords in SRW come with 3:55 or 3:35  You can't even order the 3:73  unless you get the Dually.  And folks are pulling a lot of 13,000 to 15,000lb RVs with the new trucks.  My 4H GN is lighter than your LQ but I have no concerns about pulling it with the 3:55s in my new truck. Just so much power with these 400hp/800bl torque engines.

So I'm sure the dealers are bringing in trucks that will deliver better fuel mileage while still pulling the kind of loads most folks are pulling.

We have an older SD truck with a diesel. When purchased, we had the options of a 3.73 or 4.10 axle. We opted for the 3.73 while a friend of ours bought a similar truck with the 4.10.

Whilst towing similar rigs, we run lower revs and enjoy almost a 2 mpg fuel savings over his truck. The newer trucks have more speeds in their transmissions, which means you can have both overdrive gearing and more torque available in the lower gear selections. The final revs are not so dependent on just the rear axle ratios, but the OD gearing within the gearbox.

As was stated, a 3.55 ratio and the 800 pound feet of torque the new diesels produce, will haul quite a load and get some decent milage to boot. Obviously the truck should be equipped with the suggested factory recommendations for the optium performance.