If you are pulling with a Duramax/Allison,
using Tow Haul mode will use more fuel. However, it also gives you the
transmission braking for down hills and when you are braking. It helps
tremendously to control the load. My dealer recommended that if I pull more
than 50% of the rated towing weight, I should use Tow Haul. I am right at 50%
and use it all the time when I tow. I love the control it gives me!
