I wouldn't worry about out of control sway as much as I'd be concerned about the TT and truck not functioning as one. A heavy long TT with a 1/2 ton may not ever sway out of control, but you could experience more than desired movement when over taking a semi, or being passed by a semi and towing in windy conditions. Also it could be a little tense when needing to panic stop on a corner.
Lots of conditions come into play when towing.
Having to keep both hands glued to the wheel with bigger than normal wheel corrections doesn't make for a fun day of towing.
Like I said you may never experience out of control sway, but the day in day out driving experience will wear on you.