bad vibrations

hey everyone, im having some odd vibrations when im decelerating and when i put my truck in neutral it does the same thing while coasting, i have a new ujoint in the rear and the double cardnal looks fine. I have checked my ball joints and all my brakes. Im wondering if maybe one of the front axle u joints could be bad or if maybe the ball joints are and i didnt notice, i did the normal push and pull on the tire trick and it was tight. SO hopefully you all have some ideas of what to check, im pretty capable of doing about anything on the truck just would like to have a good idea where to start so i dont dump an bunch into it for no reason. THanks