Your Freightliner chassis should not need the add-on items that some posters are suggesting.
More than likely the tires are inflated to the tire sidewall max pressure making the tires to hard.
First thing on any new coach is to weight it and set the tire pressure per the tire manufacturer chart.
Most find that this makes a world of differnce on a rear engine DP.
Second thing is to have your alignment checked. Tiffin or Freightliner will probably cover the cost.
Third have the 'ride height' checked. They typically do this at the alignment.