ok all, let me see if I can explain this without confusing myself and everyone else. I'll attach a few photos and give a brief description of each one and then try to summarize it the best I can so here it goes.
The pic below is a depiction of an axle mounted below the leaf springs (like on the Titan) in a static condition.
This is a picture of what happens to the leaf spring during acceleration more commonly known as axle wind-up, or axle wrap. The nose of the vehicle would be to the right of the picture to help you visualize what's happening.
Many manufacturers have this same problem, common cures are traction bars or ladder bars for off roaders and racers. Usually it's not as noticeable as it is in the Titan, Nissan should have used either thicker main springs or a multi-link suspension to help cure this but I'm sure cost was the biggest factor.
Here's a few pics of what I installed to eliminate this problem
Here you can see how they are just barely visible from the side
What your looking at are $22 helper springs I bought from Advance Auto Parts. I installed them in front of the axle instead of the rear like most would do. During acceleration this big beefy spring will transmit the twisting motion of the axle to the front of the spring where the attach bushing is. I've had these installed for several months now and will never take them off, that's how much I like them. They eliminated all the clunking noises I would hear from the axle twisting up and down during acceleration and when I came to a stop.
Another benefit I've noticed is they really work like traction bars because I can barely spin my tires now at take-off, but it feels like the front end is going to come off the ground.
It transmits all but a few percent of the torque directly into the chassis rather than leaving it on the ground in the form of burnt tires.
The Nissan Tech took some photos of what I did and sent them to their engineering department in California. He loves the fix but agrees that Nissan will never approve such an item for axle wind-up and that it will probably take eons before the issue is seriously looked at. So that's it in a nutshell. It fixes all the clunking for $22 and doesn't negatively effect the ride at all. As a matter of fact I can really feel a positive difference in corners, the truck stays much flatter and feels much more solid when the corners get bumpy.
I would love to stick around and see what you all think but it's night night time for me......4:30am comes early and I've still got a heck of a honey-do list. I'll check back in tomorrow night and try to answer any questions you all might have.
Dale