Where in the heck did everyone come up with a towing speed of 70 mph? Did anyone really read the OP's post? He had no issues with the Rhino in the back of the truck and no sway at 70.
OTOH he did say "I got up the top speed I will tow a TT, 65mph." And then a couple sentences later posted he got up to 70, so which is it?
But the sway occurred at the lower speed and not 70.
There is a dearth of information: what size is the WW toyhauler, what size is the truck, what size and rating are the tires on the truck, how much tongue weight is there, is there anti-sway bars, is there WD hitch involved? All the information would be wonderful.
My opinion is that of most everyone else: not enough tongue weight.