If the dealer set up the hitch I would suspect that to be a part of the problem. First, most won't take the time to actually dial it in properly. Second, if they set it up when you bought it, was it empty? Things can change dramatically once the tt is loaded up.
Load the tt ready to camp and then adjust the hitch. Also ensure you have enough tongue weight. Should be around 13 percent of loaded tt weight. Don't load the rear of the tt to lighten tongue weight. I did find that even a couple hundred pounds removed from the rear towards the front made a noticeable difference in stability.
Best to hit the scales and get actual weights and go from there. Google tongue weight bathroom scale for an at home way to get tongue weight.