Springs are what set the ride comfort, shocks can make it worse but never better
Trucks are over sprung because, in the Rangers case, they are rated for 1,400lbs of extra weight, payload and passengers
A spring works by the weight it supports
If a spring is rated for 1,000lbs and that corner/side of vehicle weights 1,500lbs then weight pushes spring down too far and you will get "it rides like a boat", lol, always leans on corners, but absorbs bumps well, lol, until it bottoms out
And conversely if that corner of vehicle weighed 500lbs then spring couldn't work at all, there is not enough weight to hold the top of the spring in place so you would feel every bump in the road, would be like not having a spring at all
So its a balancing act for actual weight and spring weight rating
The rear leaf springs on pick ups are always over sprung, so they can haul loads, but if you drive empty most of the time it will feel "stiff" because it is, not enough weight to hold springs down so every bump is transfer to the frame and body
As said you can through sand bags or extra weight in the bed, a canopy maybe, to get some extra weight to hold the springs down, but MPG goes down as well, i.e. hauling extra weight around
Or...........you can get lower rated springs matching empty bed weight and add an Over Load spring, this is a singe leaf spring that isn't used until enough weight is added to the bed and main springs touch it for extra support
Its of course more expensive which is why factories don't do this, lol
To test your current springs remove each shock's lower bolt(or upper), so no shock assist on each axle
Bounce each corner
That's your spring ride
Should bounce easily for comfortable ride
If its stiff then its over sprung, shocks can't help with that
Shocks purpose is to slow down spring rebound effect, proper rated springs like to keep bouncing, which is a nuisance, lol
Proper rated spring, without shock hooked up, should give you good bouncing
Higher rated springs don't bounce at all
You want a shock that allows the springs to do their job but slows down the rebound so they don't over do their job
Most shocks do that, nothing special is needed, off the shelf