My original rear springs cracked with the 4inch blocks...wear and tear over the years.
So i replaced them with Super Lifts 4inch soft ride springs...not rough @ all.
Smooth ride, i haven't towed yet with them i need to buy a hitch and receiver (soon).
Thats my take on those, they are kick ass!
I've loaded the bed 3times with a little over a ton with the posters (10,000 posters). and it barely squats, so this year ill install air bags.
The stock ones were so worn out the truck as really low on tough loads