You already towed the TT without a sway problem, and then on your second tow had a problem, Most likely the TT didn't have enough weight on the tongue, and had too much weight rear of the axle. In other words, it was "back end heavy". There should be 10% to 15% of total weight on the tongue. Try loading the cargo with more weight up front and I'm sure you will see a difference. Happy travels.