I think we are closer in our opinions than we are coming across in this thread. My 2011-2017 Powerstrokes have all had 3.55 gears and always held 6th gear on level ground while towing in the 9-10 mpg range. Under these conditions I sometimes find the engine might even rev higher than I like when the tow/haul is selected and so I might not even bother selecting tow/haul. When towing in long hills I will often manually lock out gears on the downhills to utilize the exhaust brake and occasionally I might drop a gear anticipating a climb. When towing heavier (I sometimes tow close to 40,000 lbs combined) my automatic starts using 3rd, 4th, 5th and 6th and I might lock out 6th to limit the back and forth shifting but it is rare that I feel the need to screw with it.... if I'm climbing I'm in 3rd or 4th and going down a bit of a grade I might be in 6th.
