I've never heard many diesel truck owners (any brand) complaining of their truck not having the power to pull. The DEF trucks just have incredible torque.
Don't get too hung up on gear ratios. Variables are the final gear ratios of the transmission and the diameter/height of the tires on the truck.
If you have the choice, get the Ford with the lowest gear ratio available. If it comes just with a 3.31, rest assured that it's going to tow your load.
And for fuel mileage, just keep it below 2000 rpm's. That's the sweet spot for fuel usage.
