Installed some Timbrens(the H.D ones) on my 2012 F-350 chassis cab on the rear a few weeks ago. They were easy to install and work well. $288 from Stengel Bros. They gave me a discounted price saying it should cost no more than a Dodge application. Could not install the 1 inch spacers as there was no room to do so. Even without the spacers, it holds weight very well. I have put up to 6400 lbs on the truck and it barely engages the overload spring. My 2012 350 can handle as much weight as my 1999 450! ( even without the Timbrens).
It would not surprise me if it could hold up to 10,000 lbs. cause I have had 7400 lbs on it in the past(without the Timbrens). I won't put over 8500 on it for safety reasons. And no the Timbrens do not engage when I hit a bump or dip on the road. I don't even know they are there till I load it up. They engage at about 4000 lbs. Once loaded, they reduce sway and squatting.
So far no issues and don't expect any.
Love the Timbrens on my 2014 F-250. Unloaded ride is stock, since the springs sit about 1" above the axle. When loaded with camping gear in the truck bed and my 900 lb tongue weight TT, the Timbrens assist the stock suspension to inhibit porpoising, roll and sway. Makes my 250 feel like a dually 350 when loaded!