Got them last friday and had them installed within 30 minutes of opening the box.
They don't require drilling or welding or anything except removing the old bump stop and utilizing those holes for the new Timbren. Unloaded I had only about 1/4-1/2 inch of space between the timbren and the bump stop "plate" and they recommend one full inch so they don't impact your unloaded ride. It's not been a problem for me.
I made a couple of trips to the timber to get wood and it handled the loads excellently. One load had to be 1500lbs or so and the more recent load was with my entire family and about 2,000lbs of Hickory in the bed. the truck handled it with absolutely no problems. engine and braking did well, no sagging at all, so the geometry of the suspension was held in check. I wasn't aimed at the sky, so that was nice, too. 2,000lbs+ is probably more than one should do, and I won't make a habit of it, but it was nice for the peace of mind for planning other things that I might not have even considered. at no points did I feel unsafe with that load, although you have to watch your tires at that point (especially if they are nearing the end of their lifespan). The axle isn't built for that kind of abuse, so I wouldn't recommend the overloading on any sort of regular basis.
All-in-all I highly recommend these ESPECIALLY if you use them for what they are prescribed for: Improving the handling of loads that were already within the GVWR listed for your truck. If you insist on doing more than what your truck was made to do (like I do) then I suppose they are also a good option.
For the easy install and the <$200 price tag delivered to my door, I can't think of a better option for me.
Can you tell there is about 2K lbs of hickory in there?