I have tried putting the rear tires on the front with no change, I have checked the wheel bearings which seem to be ok, I will check the bushings a little later, the vibration is a shimmy that is worse around 45 to 50 mph, and road conditions seem to affect it. and No this is not the sig truck, that is mine the problem truck is my dad's and is a 04.5 DRW 3500 crew cab with 381,000 miles and other then the 19.5 wheels has a stock suspension it is one its 3rd set of wheel bearings if you count the factory ones, all tie rod ends have been replaced several times, the u-joints in the steering knuckles have around 30,000 miles on them and are grease able and lubed every oil change same for the front drive shaft, the steering stabilizer has around 40k on it, and is not leaking beyond that I don't know how to check it, the shocks are older I don't know the mileage off had but they aren't leaking.