Sounds like your shocks may need replacing?
These are not very expensive and you will like the new ride and feel over the stock shocks. I would also replace all 4 if this is a good time, but for sure replace both front shocks on this repair. Also, I don't think you have to spend the money on Koni or other so call "better shocks." This is because all shock manufactures have improved their design and functionality and performance.
My diesel pusher shocks went out in the front last summer and I went with Monroe, because that's all the Freightliner dealer had and I did not want to wait 3 days to source another highly rated shock. And it turns out like the Monroe ride better! ...I.e., its smoother on the flats and handles the same in the corners. Time will tell, but at $125 for each Monroe shock I'm happy.
2004 Itasca Horizon ISK-40AD, 350HP Cummins 8.3L
115K miles and the best of 3 Diesels I have owned thus far!