Poor tow vehicle ride pulling trailer on certain highways

Try driving on I-10 through Louisiana. We drive back and forth all the time with the same TV and differing trailers enough to know for which sections of road to slow down

My theory; Its all due to the perfect combination of 1-speed, 2- axle distance, and 3- weight (kinetic energy) EDIT 4- the stiffness of the veehickle springs (and shocks / struts)