Rob,
You know I agree with you, right?
I am actually expecting a slight decrease in fuel economy not an increase.
As for the increased capability of the truck after the installation of a new gear set - I know that there is no linear relationship with rating, and said so. I merely was bringing up the rating of a factory 3.42 truck for comparative purposes for what can expect regarding tow ability (and power train longevity, perhaps) before vs after the mod. Of course changing to a lower gear as the need arises will still be there, rear end gearing notwithstanding.
Ratings are not simply due to gearing capability, but must also consider the entire capability of the power train as a whole over the period the manufacturer is prepared to warrant and (I would expect) the reasonable life of he truck to the owner, along with other less tangible aspects (again, I would expect) as towing ease and confidence, etc. lets not forget marketing influences as well.
BTW, all of this is my opinion as a practicing engineer since like most here, I have no direct insight into how manufacturers assign ratings.
