Hmmm... how do you know it's only driver side tire vibrating at 55-60 or is it the whole front end??
To check for bad Ball Joint, jack the front off the ground and grap the tire at the top & bottom and rock back & forth, watching the Ball Joint for any excessive play. If that looks ok, then I would check your axle u-joints for the front, physically out your hands on them and try to move to see if play in them. After that I would then check your front & rear driveshaft U-joints. Sometime with these it's best to get the weight of vehicle off the ground to check for play.
I had a bad rear DS u-joint and took a about a week or two to track down, since the weight of the vehicle was actually holding the broken u-joint together and over looked it a couple times, until finally lifted the back off the ground and saw where it was cracked.
Try looking at those few things and let us know what you find.