Vibration while braking

[Rannos]

I recently bought a 2005 silverado ext cab with the lq9 6.0. Truck has about 55k miles on it now and has an intermittent vibration while braking. It did this when I drove the truck at the dealer and they turned the rotors and installed fresh pads. When I came back to pick it up it seemed like it was cleared up but now its intermittent. I can drive all day and it may only do it once or twice or it may do it almost every time I stop on my way to work (25miles). I pulled a front wheel off and spun the rotor with an indicator on it looks good. Recently it has started to get worse and seems like it starts up front and the vibrations travels to the rear of the truck. I have no idea what could cause this. If anyone has had a similar problem and can point me in the right direction I would be grateful.