To answer a few of the questions, I try to tow between 68-72 mph locking out 9-10 speeds. My speed depends on traffic, road surface temps, and headwinds only due to gas consumption (I am cheap). My speed also depends on how soon I want to get where I am going. Somedays we did 400 miles, other days we did 600 miles.
I am thinking about adding the Hellwig sway bar, I added one to my 7.3 Excurion.
As for longevity, well its got a 200,000-mile warranty on the drivetrain and I buy and sell my vehicles about every 80,000-100,000 miles not because I need to but because I am normally bored with it.
All in all the 3.5 and 10 speed is a great combo.
