I installed the Thuren Fab kit. It's awesome and I highly recommend it. The increased travel and articulation of the suspension makes a huge difference off road. I can now drive through stuff in two wheel drive that I used to have to lock in to drive through. Relative to the comment about installing these kits in trucks designed to haul, I have a couple of comments.
1) While I am no fan at all of installing lift kits because they look cool, and I hate the *** dragger look you see it seems on every lifted Ford, there are kits, Like the Thuren, that actually significantly improve the truck's off road capabilities. The full Thuren kit lifts the rear as well, so most of the rake in the stance of the truck is maintained.
2) Yes, typically unless you are installing a spacer lift, the load capacity is affected but the truck also rides much better, and performs better off road.
3) This is the biggy for me. Yes these trucks are designed to haul, but not everyone's hauling needs are the same. For me, my truck needs to haul an expedition camper I built, and it needs to do it in high mobility off road situations because my son and I do a lot of overlanding. Yes, I've traded some ultimate load capacity for long range comfort and performance off road with the lift, but I have gained that capacity back with a custom air bag setup that is highly compliant off road and doesn't limit the suspension travel.
So in closing, as I said before, I'm no fan of all the stupid under performing lift kits designed for no purpose, other than looking good and fitting big tires. Kind of like the stupid exhaust stacks sticking up through the bed of the truck. However, some of us who lift our trucks and install larger tires, bumpers, etc, do it for reasons that are different, but no less an appropriate use of the HD truck than setting it up to haul a giant land yacht down the freeway. Different application, that's all.