When is a good instance where you would want to lock out OD? Excessive inclines where the trans is constantly down shifting? It seems like the 6spd would shift more often anyway since there is an extra O/D gear.
Wait a minute. The 2011 (6 speed) I have has a Tow/Haul button on the Shift ****. It does more than lock out overdrive. Which really it doesn't. Apparently, according to the owners manual, there are sensors that monitor the attitude of the truck so that when it is going up. It will shift out of OD and stay there prior to hitting the hill. Also on the decent, and it works pretty well, when you hit the breaks it will down shift. You can then remove your foot from the brake and let the engine keep speed. Just as you would manually.
Not sure when this was added but obviously different than the older ones.
No "tow/haul" on my '07 XLT. Nor have I ever locked out OD for other than a short experiment. All it does is run the truck at nearly 3000 rpm when it could be loafing along at 1800 rpm.
The transmission shifts frequently between 5th and 6th with an occasional drop to 4th towing my 5000 pound camper across the mountains on the PA turnpike, but the transmission temperature stays under 190°F. Heck my Expedition will downshift to 5th on these same grades without the trailer.
The uber-low 1st gear on the 6-speed seems made for towing.
I spent the extra $300 on the HD Tow option for this truck. And 5000 is well under the 9000 pound maximum towing capacity. Pushing the high end will probably be different.