Failing to realize that stiff framed trucks tricycle off-road, making them less capable. This is what this post is about. Actual off-roading... not traveling great distances on road. Thank you for continuing the story and your feedback.
Failing to realise that a truck frame is NOT suspension is common is this community. It is an undamped spring. Speak with any race car, mountain bike or vehicle engineer worth his salt and he will tell you, if he's honest, that tuning a suspension on a flexible chassis, frame, tub or monocoque is a nightmare. The stiffer the frame, the better the suspension works.
The reason that these heavy-duty trucks "tricycle" which is a noun, not a verb, is that the suspension is designed to carry heavy loads with minimal wheel travel. These vehicles, e.g. Ford's F-550, do this very very well. If they were designed to articulate or have massive wheel travel (Can Am X3, downhill mountain bike or trophy truck), then they would do that very well. That was not the design brief.
Don't conflate a bone stock or mildly modified truck designed for carrying heavy loads (work truck, ambulance, roll back wrecker, agricultural use, heavy towing, etc.) with a rock crawler or even a Unimog. The latter has absolutely abysmal suspension. Have you ever ridden in or driven one? They are dump trucks compared to a modern light duty truck or SUV. Mercedes designed the frame to flex because the engineers could not figure out how to carry heavy loads AND make the suspension flexible at the same time way back in the 1950s and 60s.
A flexible frame is an undamped spring. It is not suspension; it does not suspend anything. That is the job of everything below the frame, e.g. leaf springs, link suspension with coil overs, air bags, etc. A leaf spring is also an undamped spring, which is why it's always paired with a damper or shock absorber (a shockie for our truncating Australian friends).
Big heavy trucks ride like crap because they are designed to carry heavy loads, by the OEM. They are not designed to ride like a Rolls Royce Ghost or to bomb down a dirt road at 60 MPH.
Horses for courses.
P.S. You may wish to read Doug Hackney's posts to see what happens when a heavy frame flexes one too many times.