We used Timbrens on our '16 Ram 3500 SRW (SRW has no upper overloads) for a short while. They work well to reduce sag, as long as you take the time to optimize the spacing between the Timbren and axle housing. Too much space reduces their effectiveness, too little space harshens the unloaded ride. Unfortunately, our camper is heavier on one side, so we replaced the Timbrens with airbags.
We found airbags good for sag (plus each side is independently adjustable); however, once they're inflated above 25-30 psi they tend to get "mushy" with reduced side-to-side stability with a 3-4k in-bed camper on-board. Decided to try a set of lower Torklift stable-loads (stainless steel versions). They helped with sag, plus they increased stability because they mount more outboard then the airbags. We've found airbags (at 15-20 psi) and lower stable-loads are a great combination--providing reduced sag and improved overall stability.