Yup, tow/haul mode and let the truck figure it out.
Check your trailer tire speed rating. Most are under 75 and many are 65.
I’ve found noticeable mpg differences in each 5mph increments above 55mph from TT vs. wind resistance. Around 65mph is my compromise sweet spot towing the TT for reasonable speed (time getting there) and mpg (10 mpg plus fractions) and not being a too slow road hazard. I say around 65mph because I let gravity do it’s work downhill and not sweat the speed drop too much uphills (but I try to stay above 55).
