So far, the kit is holding up great. Pretty simple given it is the metal spacer (1.5" under the lower shock mount) and I used 2 of the .25" spacers on top for a 2" lift). Ride is same as before I lifted and I love the look. I first took it to NTB and they couldn't get it aligned. They simply didn't know what they were doing. Went to my local 4WD place and used their alignment shop and he said he was a piece of cake. I've only had it on for 2-3 weeks at this point, but couldn't be happier.
I don't do a lot of off roading other than my 1/3 mile gravel drive up a hill, but it handles all the bumps and stuff just like it did before I put on the level.
It would take more than the 2" to level my Denali, but I tow so I wanted to leave a bit of rake and I didn't want to go over 2" with the leveling kit.
Right now, I have the stock 275 55 20s on the truck. It looks OK, but not great. I have a set of cooper A/T3s for it in 275 60 20, but I haven't had time to get them installed yet. I thought about going with a 295 or 205 55 series, but the additional cost of those tires just wasn't worth it for me. I got a great deal on the Coopers from Discount Tire Direct using their price match. After rebate, they were $630 delivered. I think it will look a lot better jumping up to the 60 series.
Mike