99 Ford Ranger "shakes at 60 mph"

[Ford Ranger 99]

My truck shakes as soon as I hit 60 mph....if I drive under/over 60, it stops....what gives? At first I thought the ball joints were worn out, so I had those replaced. Also had an alignment done just in case, but not much of a difference. Anyone know what it could be?:rangertan:

 

[94xlt4.0]

sounds like the tires are out of balance, i would get that checked before doing anything else

 

[McCormack]

Tires out of balance or possibly a belt starting to separate.