If the shutter is from the clutch, which is likely, then you might try the method I used to cure the shutter on an old truck I once had.
I tied an old tire to my front bumber and eased the front end of the truck up to a large tree in my yard. I then slowly let out the clutch to cause it to slip. I don't know if this made the whole clutch glazed or wore off the glazed areas of the cluth, but it cured my shutter problems.
