Did this car always do this or did it just start happening?
There are several different reasons (and cures) for hard shifting. How many miles on the car?
You can adjust the timing of the shift by adjusting the transmission bowden cable, but the firmness is a result of pressure.
Does it shift hard through-out all gears?
Have you expereinced power loss?
It could be the vacuum line and/or the connector going to the vacuum modulator on the transmission. It could be the vacuum modulator itself. There is an adjustment for the pressure on the side of the transmission, but before adjusting that, I would make sure you don't have some other problem.
Keep us posted,
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