The biggest issue you will face is the wind. Due to the high face area of the TT, there is a lot of drag. We don't have issues until the winds pick up. At that point, the tow load is a little higher, and I find the transmission hunts from 4th to 3rd alot. Wind causes alot of sway, as well.
Always drive with the OD off. I also find that if I drive at 90km/h, it tends to cruise a little better, though this isn't always an option, and the truck has no issues getting up into higher speeds. Don't expect to get better than 10 MPG when towing.
We don't tend to go more than 100mi from home for now due to having small kids. Once I have a tranny temp gauge installed, I will be be more than comfortable pulling longer distances (provided the tranny temp isn't getting too high). Its also very flat here in Manitoba, so if you are in the hills or mountains, you may need to be patient on steeper grades.
However, my concern is always more about being able to stop than being able to go really fast.

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