I have a 2.5" level kit on my from Top Gunz. We put the truck on a lift and used another jack to cycle the suspension as far up as possilble and let it hange all the way down and I could not make anything hit. I am only running stock 275/70/18's so if you are going bigger then it may be an issue.
I have a 2008 KC Pro-4x and I was told that the bump stops were for the 2wd trucks with softer springs.... I have no idea if that is true.