Transmission shifts hard in hot or cold conditions

Sometimes l have to pull over because there is a loss of power. I turn it off and restart it and it acts like nothing happened. The transmission does not act like it's slipping at all. It's like when it's suppose to shift in the last gear it doesn't shift right with the rpm of the motor and when it does shift it shifts super hard. Does not do it every time either. Most of time it's fine.