shaking
You said the tires are balanced, but when were they last balanced?
new clutch?
hit any potholes?
you may need to have the alignment done, you may need to have the tires balanced again, maybe have them pulled off the wheels and switched from one side to the other (assuming directional tires) if you've changed anything else that rotates (like the clutch, driveshaft) there may be a need to have it checked for balance

