Don't limit your trouble shooting to it being a clutch issue. When you are stopped in gear with clutch all the way in, does the car want to creep forward? If so, the clutch is not releasing. If no, then it might be something else that is causing hard shifting.
Having the wrong gear oil in the box has been known to cause hard shifting when the fluid gets hot. You want plain Jane API GL4 or GL5 80W-90.
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