With gas engines, you need to let them build rpms to generate HP. HP is what determines how fast you can climb a hill. Torque determines if you will make it up the hill.
With the 10 speed transmission, rear diff ratio really doesn't matter unless you are pushing the truck to the limits. The transmission will just pick the gear suitable to get the overall ratio the engine wants.
Presumably you are running at around 11k lbs loaded. That's well within modern gas truck capabilities and tow haul uses engine braking pretty effectively with gas engines.
Of course if you are just trying to justify what you want....just buy the diesel.