Front end shimmy on 1997 Ford F-150

I have a 1997 F150 4x4 that has developed a shimmy problem at 35mph & above. It has new ball joints & stablizer bars installed about 18 months ago. What is most likely cause?

Asked by for the 1997 Ford F-150
Recommend recheck front end for any more loose parts. If shimmy is at higher speeds then could be tire balance. Is shimmy in steering wheel or seat of your pants? Tire wear problems can cause shimmy. Have looked at.