Did you check the shocks? If they are OEM, they went bad long ago. For that old of a Bounder, consider using Bilstein's. Their aftermarket shocks usually go on sale a couple times a year and are adequate for your rig.
The wagging is often due to shocks. But it could also be due to low tire pressures. You should try setting your tires at the max shown on the sidewalls.
And what do your steer tires look like as they age? Any unusual wear patterns? Again, low tire pressure can make steering difficult in these big wind pushing boxes.