We just put a 6" lift, with 35's, on our 08 1500 2wd Silverado.  At low speeds there is no problem, when we brake at higher speeds the truck vibrates hard.  The dealer checked the alignment, said no problems, yet it still vibrates.

What else could it be?  

Never mind, we forgot to remove the factory tabs on the brake calipers.  Removed them, it solved the problem!  

Hello, I just put a leveling kit and 33" tires on my 08' Silverado. I have the same problem with my brakes. I just want to know you did to fix. I know you said you removed factory tabs on the brake calipers. Please explain. ??????