I'm not a truck person, but read your owners manual and/or door sticker for tire pressure, empty and loaded. If they are overinflated for the load they are carrying, you will get the ride you are describing. Best would be to get the truck weighed fully loaded with trailer, front and rear axle plus trailer axles. Then have the truck alone,as your daily driver weighed, again axle weights.
Then use the tire manufacturers chart for your particular tire to see the recommended pressure for each tire/axle. You might get a smoother ride for next o $0.00
Ken