Hi everyone new to duramax trucks I looking at a 2006 GMC Sierra K3500 4x4 Crew Cab diesel with a contractors bead, are there any difference in the C or K? I think it was a cab and chassie when new.Does the K still have 4 wheel disc brakes? I live 1000 miles away from the truck so right know pictures are all I have to look at. Any question I need to ask with common problems ? Thanks