Bob,
You are on the right track with your top two.
Most critical is tire pressure to assure you don't get a blow-out. Based on your dry weight spec of 9400 pounds which is the same as our rig, I would start with 65 psi in all 4 tires as that is what I run with. Maybe even start with 70 psi. If it's too much, you won't do any harm given they are "E" rated tires with an 80 psi max rating. 55 psi seems alarmingly low, at risk of blow-outs and significant handling troubles.
Adding a heavy duty rear stabilizer will do wonders. Don't yield on that addition. A Helwig will be more affordable than a Roadmaster.
Everything else can be done after a thorough evaluation of the top two. If your rig could still use extra help, consider heavy duty RV shocks and a heavy duty front stabilizer bar.
Front & rear heavy duty Helwig stabilizer bars are affordable and are DIY friendly....especially the front bar. Heavy duty shocks can be pricey and not so DIY friendly, primarily due to rusty mounting bolts.
If it were me, I would get the tires up to 65-70 psi and install both front & rear HD Helwig bars and HD shocks. Then re-evaluate afterward. You won't be throwing away any money with that investment of around $750 in parts. Not only for driving comfort, your rig will be much safer to drive. It will remain more firmly planted on the road for improved braking power when on mountain and canyon byways. That is very cheap insurance that unlike all other insurance policies, it also pays in passenger comfort and reduced driver fatigue. It even pays while parked with less need for stabilizer jacks.
If towing anything, you might need to invest in a rear trak bar which eliminates the "Tail Wagging The Dog" condition. That condition is magnified with a long rear RV over-hang, rear of the rear axle along with a standard wheel base.