I have a 2003 39s Discovery I believe built on the same freightliner chassis you have. Your issues a identicle to what I experienced when I first bought my unit used with 28000 miles on it.
Do the following:
Replace all shocks with Koni FSD shocks, about $800 installed.
Install the steering stabilizer from Steersafe of Demming NM. About $400.
Have an alignment done.
Make sure your tires are at least 275 size and inflate to about 95PSI cold.
I did all of these and the coach is now well behaved and can be driven all day with one hand.My current odometer reading is 73000 miles.
Bob