In my Hilux LN106 Pickup the gear shift lever is oscillating severely (left-to-right and back) when driving at 60kmph. It disappears when speed reached 70kmph.

The most recent changes were the pressure plate replacement and Drive shaft U-Joints replacement.

What could be the reasons?

 

I don't know what a ln106 pickup is but in my 90 sr5 I had the same thing happen when I had a tire/wheel out of balance. Might check the balance on your tires.