Mystery Product

I recall while watching one of those automotive shows, about a product that worked in conjunction with a pickups rear shackles that softened the ride considerably. I believe it was Shadetree Mechanic or Two Guys Garage. Don't remember which. What I do remember is that the device acted as the rear suspension until a load is put in the bed. Then the device compresses and the shackles take over.
Anyway, does anyone know what this device is called and where possibly it can be purchased. Thanks in advance. Mark