I also posted on this question in the truck form.

Whenever you put the trans in Tow Haul or OD off it disables the MDS system so it doesn't drop cylinders to "help" fuel mileage.

I had an 08 and on my 11 mile commute my MPG didn't suffer any running in tow haul(no MDS) or regular.

The MDS was almost overactive on my 08, it would come on at low speeds even in my neighborhood. The MDS could sound like a miss at low RPM for sure but it should turn off when any load is applied(throttle).