[kaisen]

Yes, that's correct. A 4.10 is not better or worse than a 3.73, it's just suited for a little different work. A 4.10 will pull better in top gear at, say, 60 mph where a 3.73 may pull better at 70mph. If you're going to be towing at 70mph all the time, then a 4.10 might be the wrong choice. Just an examples, there's much more to it as Angela pointed out. Tires, power curve (torque peak, area under the curve), transmission gear ratios, etc.

With the GM 6.0L and 6 speed automatic, it's not as important. The difference between 5th and 6th gear isn't great, so even if the 3.73 forces a drop in gear, it's basically like a 4.10 in 6th (if that makes sense).

A 4.10 might make a numeric multiplication of torque/force, but won't make up for the difference in the power curve. In other words, a 4.10 at 75mph may push the revs higher than peak torque. You want to pull at peak torque.

FYI, a Duramax diesel's ONLY gear choice is 3.73. Think about it. If a 4.10 were automatically 'better', wouldn't they offer that choice? And if 4.10 is great, why not 4.56? Etc, et al. It's a system. And there's a lot more involved than just the final gear ratio.