If it tows fine in all other conditions and this was a one off occurrence. Slow down. The wheel bases of the truck and trailer may be 'in tune' with the pavement undulations causing the issue. This is assuming that the truck and trailer are properly set up. Better yet get off the interstate and use US highways which generally are a much more relaxing drive for both the equipment and driver.
'19 Outdoors RV, 21 RD Titanium, Equalizer 1K/10K
'18 Ford F-150 V8, Magnaflow, 10 Speed, 3.55 locker, Tow Pkg, OEM Brake cont., 36 Tank, 1900 lb Payload, Roadmaster AS, 5100 or Falcon - can't decide.