No one is buying a EcoDiesel thinking it is going to out tow a Ecoboost up a hill or even in the flats, not going to happen! However it will tow it's rated load without any issues and there are plenty of guys towing a whole lot more then I would tow with it without any problems also.
As far as the EcoD longevity goes, it's a diesel and a well built diesel. Like all diesels they are made to run all day long at red line without harming the engine. Don't think so? Look at big rigs they run up the same grades with the peddle to the floor and clock 500K (if maintained) before needed a rebuild. I used to run from Toledo to Murfreesboro, Tn and Toledo to Owensboro, Kn three times a week when I was on layoff. The truck was governed @70 mph and had 450K on the clock. The only time it was not to the floor was on the flats or going down hill. Average load was 42,000# to 48,000# and she ran like a top.
I wouldn't think twice about towing a 7,400# RV with my truck. Funny thing is there is a video out of the Titan 5.0 CTD towing at it's rated trailer max and it can't maintain the posted speed limit on the Ike and no one said a word about that. We will see what the 2017 F-150 3.0 Diesel does and see what the Blue Oval Mafia has to say about it.
Don