^ First, over drive, underdrive, direct, are nothing magical. They're only gear ratios in the transmission. That is literally only 1 of 4 parts of the overall gearing equation.
But the real answer is you haven't seriously driven, or towed with similar vehicles with a 3 - 4 - 5 - 6 - 8 or 10 speed transmission.
It's akin to cutting down a tree.
You can do it with a hatchet = single speed, a hand saw = 2 speed, a felling axe = 3 speed, sawzall = 4 speed, little chainsaw = 5/6 speed or a Stihl 460 = 8/10 speed!
It's one of those, don't know what you're missing things. Do I miss a 6/8 speed trans in commuter traffic or driving an empty pickup? Nope.
Does the 8 speed in our new SRT click off shifts in under 2/10 of a second when you mat the skinny pedal, up AND down shifts? Yup.
Does the 6 speed in my little 1/2 ton work truck tow better than the 4 speeds in our older 3/4 tons? Yup