Speed is one of the biggest factors when towing. I have 7500 pound empty or 9000 lbs loaded I usually average between 11-13 mpg on flat ground or 10-11 mpg for the long pulls around Mattawa, Ontario. I always use the tow/haul button and lock out 6th because I find it too tall of a gear for the long pulls 90% of the time I use cruise control and let it do its thing. I always keep it between 55-60 mph ...I find that after 60 the fuel economy drops quickly. My truck is a 2011 eco Max tow with 3.73 rear. Sorry ...and yes it is normal for the truck to downshift with the cruise it will try to slow down the truck. After a while you will get use to the downshifting.

 

Care to elaborate?

 

You want to use Tow/haul mode when ever you are towing. And yes it also helps with prolong the life of the transmission. Even though Ford does not say you have to use it but for those people that keep their trucks longer then 5 years is where using this helps. I know for GM it increases the line pressure which gives you that 'quicker' shift feel. Its because slippage=heat and the more heat in the transmission the worse it is. When you shift hard and fast, you actually prolong the life of the internal parts. I am sure in the Ford tranny it really is no different. Yes, in the 700r4 I wouldn't tow in 4th but in this ford I would as long as the road I am on is flat or relatively flat. If I was in a hilly area, I would remove 6th to minimize the gear hunting which is also not good for longevity.

here is some info on the ford tow/haul mode and its benefits in general.
http://www.intermotive.net/Tech%20Ti...ugust%2006.pdf

 

the article above is rather dated, and is written for the transmissions of the time, mostly the 5r110.

here is ford's info for the 2011 tow/haul specifically for the 6r80 in the f150
2011 FORD F-150 TRANSMISSION FEATURES FASTER, SMOOTHER SHIFTING, BETTER FUEL ECONOMY | Ford Motor Company Newsroom