Ok, in each gear, going down the road at about 2500-3000rpms, let off the gas and reapply the gas while watching the movement of the shifter. Normal movement is only a slight rocking from side to side. If the shafts are moving front to back per KevinC, you should see the shifter bumping fore and aft.

In my experience with the KM145, the next step for yours is a loud shriek and a loss of either all gears, or all but 4th and revenge. With no more warning. I told you so x 3...

Not responsible for advice not taken...