jw,
there is more to it than just the gears,
what about the heavy duty cooling system, larger transmission with cooler, cooler, larger brakes, heavier tires and frame, etc:
check with ford, what came on a truck ordered from the factory with the 4:10 differential.
compare cost, it may be cheaper to up grade the truck, if you have a nice truck it will bring a top dollar on trade in.
I have a trailer much like yours, I was never satisfied until I stepped up to a 250 or 2500 series truck,
on a 3/4 ton, you get more than just pulling power, you get larger frame and bigger brakes, which is most important to me, being able to stop the load and handle the weight in windy conditions.
what we did and its a much more comfortable tow.
now we pull with an extended cab 2500 dodge diesel, boy o boy with that diesel power, extra length, extra weight of the tow vehicle, you really feel the power and control and still get good fuel mileage.
be safe out there,
you cannot have enough truck, when some fool pulls out in front of you and you have to shut her down hard and fast!!!!!!!!!! you need weight and brakes
or you are pulling up into the smoky's with (5) 18 wheelers on your tail