1995 Honda Civic Shaking since cluth replaced

I recently had my clutch replaced and was told all new belts and bearings were also installed and the flywheel was resurfaced. I now cannot downshift from 3rd to 2nd or 2nd to 1st without the car seriously shaking to the point where I need to grip the stearing wheel with both hands. What could be causing this problem?
Service Tech said I should change my driving habits and just use the brakes instead of downshifting to slow down. I've had this car for 15 years and have been driving this way and this is the first cluth I've had to have replaced.