I own a 2007 Dodge 2500 4X4 with a 5.9 Turbo ...

I own a 2007 Dodge 2500 4X4 with a 5.9 Turbo Cummins Diesel w/4sp auto. I have been experiencing an occassional violent vibration/shudder usually after hitting uneven pavement at highway speeds of 65 to 75 mph, BUT have had the same thing happen at speeds of 40 to 45 mph but not as violent. I have had the vehicle in to the dealer 3 times for this and they assure me that everything is okay, and can't explain the reason for this to happen. I have not modified anything with the truck and it sits as it was when purchased. The dealer had to replace the power steering box and steering gear box last January because of failure. They also replaced all of the tie rods and drag link to beefier construction because the truck was purchased with factory lift and leveling blocks. I am very concerned about this violent shuddering because last Thursday it happened about a dozen times in about a 20 mile stretch. If anyone out there can point me in the right direction to fix this, I would be greatly appreciative. Thanks! timhadrych@gmail.com