Basically - on the F53 chassis, it could be a number of things, or combin=bation. As other have suggested, maybe do the CHF, first. The F53 chassis is notorious for bad handling / ride (I know, as I have one). I am assuming you probably have a 22K F53 Chassis on the 28' MH. Possible fixes"
Tire pressure via 4 corner wright
Add Sumo Springs
Add HD front sway bar
add add'l rear sway bar(s)
Replace shocks with Koni FSD units
And you could add a rear trac bar to prevent swaying form passing trucks, etc.
Rather than just go to a RV repair facility and have them slap a bunch of stuff on, you may want to see if there is an authorized dealer for Henderson's Line-Up in your area that can do an assessment of what your issues are and what you need to have done. You can do this a piece at a time, with highest recommended first, or all at once. We had a brand new class A on the F53 chassis that we took to them, in Grants Pass, Or, last summer and they resolved all of our sway, porpoising, lane changing issues. It was not cheap, but we now enjoy traveling in the MH a lot more than we did before.
