truck vibration???

[Sean M]

i have a 2003 f350 the other day it developed a shaking/vibration when i slow down. the rear caliper had been sticking here and there so thinking that may have been the problem i changed the rotor and caliper but it still does it? the truck doesnt do it when accelerating only when decelerating and it gets worse the slower i go and if i hit the brakes it gets a lot worse. i put the truck in neutral and does the same thing i took it to the dealer and they said they dont know what it is he said maybe the rear dif which i dont think it is or he said hes just guna have to throw a bunch of parts into it til he fixes it so i took it home and am trying myself. any help i would really appreciate thanks!

[Banshee34]