I first towed my 6500 lb TT with a few hundred pounds of gear in the bed at about 1000 miles.

Towed again last week with about 2700 miles on my 2014 F-250 6.2 CC SB gasser. Noticed that the throttle response seems to have improved as did the ease of towing that load, especially going up grades.

I realize that it is a subjective observation, but I think the truck has significantly improved its hauling performance after a break in period.

 

There are several comments throughout this forum that support this statement.. I too noticed differences at 500, 1000, 3000, and now at 10,000.