While leveling kits can cause issues, your leveling kit is not causing this issue. I've been through 3 different dealerships, 2 GMC, 1 Chevrolet, at the recommendation of the case manager at GM itself, and they all went through the same gyrations, until a GM field tech was finally called in to do what they do best: Stamp the case as being "normal for this type of vehicle", seemingly to try to setup a legal defense. If it was "normal" why did they have me go to 3 dealerships and have a field tech come out?
FWIW, the service manager at the Chevy dealership personally inspected the shocks to ensure something wasn't stuck up under their "sleeves", too, because he was puzzled by it. But, once the field tech came out, the service manager's hands were tied.
I have two sets of OEM Denali wheels. Stock 22" and 20" with stock tires. Although the vibration is still there with the 20s on the truck, it's a little less noticeable so I run the 20s for the dry season. Because the stock 22" tires are way better for wet conditions than the pseudo-AT stock tires on the 20s, I suffer the more noticeable vibrations and run the 22s for the wet season. I'm a little more fortunate than the next guy, I think, because mine vibrates between 68 - 81mph, so I tend to drive at least 84 mph on freeways, true to my forum username. While I'm living with this vibration for now, I will never buy a GM 1500 truck again. None of my friends with 2500s have this issue. Even so, if I ever buy any GM product again, it won't be without being able to take the exact vehicle I would buy for an overnight demo, so I can put it through its paces.
Regarding ARC, ARC seems to cause fast vibrations, like reveberations, when you encounter little road imperfections. I'm sure you experience it, because when I was test driving models, I noticed that all ARC-equipped models did this, regardless of engine model. The WT and AT4 models I drove did not do this. But, at the time, I did not notice the high-speed vibration, and I wanted a truck that with the best handling and ride, which is why I went with the Denali. But, I think other people who posted on these threads have non-ARC vehicles, so I stopped chasing the theory of it being ARC-related.