I'm far from an expert in this area, but after a similar feeling when I first purchased ours used:
1. Check air pressure, then how you are loading. Try it both empty/dry and loaded for differences.
2. Go to a service center that deals with RV's and trucks. I learned a lot when they did a drive with me, as they have driven dozens and can compare the feel to their other experiences.
3. Let them do a good check of everything underneath. Make a few repairs, one or two at a time. Test drive again.
4. Only consider more costly upgrades after you know things are working as they should first.
Wish you the best....