You're forgetting that having six gears that span the same ratios as five give you closer spaced gears that allow the engine to stay in the power band better. Constantly Variable Transmissions (CVT) many times can exceed the efficiency of a multi-speed automatic because the engine can constantly stay in its sweet spot verses going in bigger steps. Not being able to use your full gear range on a full time tow rig does not make sense. Now if your truck is also driven often while empty, then there is some merit in having a gear that is not used when loaded to tip performance toward empty use.
