Tow-Haul mode makes the Exhaust Brake kick in... from what I understand Ford's thinking behind this was the brakes on the truck are powerful enough to stop the truck by itself, without having to cause added pressure and wear on the turbo from the exhaust brake adding back-pressure.
Also, you will notice if you pay close attention to the fact that when you brake(unloaded) the truck will downshift, it holds a higher gear and then drops 2 gears instead of dropping 1. Allowing the RPMs to shoot temporarily to the 2500-2700 mark and use engine braking without putting added back-pressure on the turbo.
Once you notice these small quirks, the truck becomes even more fun to drive, and you will notice less wear and tear. If you are driving in a 40-45 mph zone for instance and have the 3.31 or 3.55 gears, your truck will shift into 6th gear but struggle to maintain speed and/or accelerate. The solution for better fuel mileage and less trans slip is click the (-) on your shifter stalk until the 6 disappears off your gear display. This will keep the trans from shifting into 6th and making the motor lug. You will see increased mpg and less trans wear if you do this.