Ford did put the 17 inch tires/wheels on F450s for a couple of years (I believe 2013/2014) - they have a higher speed rating than the 19.5s. However, I hope no one is pulling at 85 mph or higher; 70 - 75 seems plenty high enough for me -- and that is driving solo on Interstate.
Tires are speed rated at 75 mph by Continental.