Continuing this thread with myself
Had the chance to load it up with 6 teenage boys and their gear for an out of state XC running event. Unlike the stock coils that just collapsed under the weight, the 862's held up as they should. Also took a 300 mile trip with kids and dogs over the weekend and again, everything held up properly.
With the stock coils, I was getting a lot of feedback from the rear suspension to the front that is now gone, handling is crisp even fully loaded with passengers and gear, ride is still very smooth. It's not a particularly taught suspension with the Bilstein shocks, but again, the front really isn't super tight either and part of of the point of a large SUV is a smooth ride. I've taken it unloaded on a short bit of rutted road and things are vastly improved there as well - all of that feedback from the rear is under control.
At this point, having done 5100's, the 862's are by far the biggest improvement to handling and ride. The much maligned Bilstein 4600's still seem nicely tuned to the front 5100's with the coils no longer wallowing all over the place so I don't see any reason to throw good money out at this point to replace them. I don't know what these trucks were like new, but those rear coils are woefully inadequate for the general intent. I have since thought about doing OME 885s for the front, but just not going to bother since front to rear is properly balanced and I can level it with the 5100's.
Light Racing UCA arrived today to handle alignment duties. Pretty stoked - it feels like a real 4x4 now.
One point of interest - since the top coils are "dead" (stacked), somebody who wanted less lift could have a shop cut them down an inch. I don't see any reason for it since it looks great and handles fantastically, but could be easily done and trimming the dead coils won't affect the spring at all except to shorten it at full droop. The rear swaybar would stop the down travel well before the coil ever dropped off the tower so there is plenty of room to trim and it's not a load bearing part of the coil at static ride height.
Hope that helps anybody on the fence with these coils.