The problem manifests itself as a distinct wobble, shimmy, or shaking when accelerating from a full stop. It is only noticeable when slowly accelerating and is not evident during a faster take off. I have had in the the dealer's shop four times for this issue. Initially I complained of an out of balance or out of round wheel. Upon investigating the problem, the shop determined that the problem did not involve the wheels or tires. They replaced the transmission mount and installed 1/2 degree axle shims on rear axle. After no significant improvement, on another occasion, they replaced the rear leaf springs and spacers with nuts and U bolts. Again, there was not significant improvement. After a total of 4 trips to the dealer shop, driving three different loaner cars for a couple of weeks, total, the problem persists. Ford Corporate has advised me that the problem does not negatively affect the performance or capability of the vehicle. This truck has a 6 1/2 foot bed and supposedly, some shudder is normal and should not be considered a defect. I traded in a Lincoln long bed truck that had no such shudder. I do not want to drive a truck that wobbles and shudders to such a degree that it is noticeable to my passengers. I am embarrassed when friends or associates riding with me notice it and comment that there appears to be something wrong with a tire.