1) Check the transmission fluid level and make sure it is right.
2) When was the last time the transmission oil/filter has been replaced. Sometime, new oil makes miracles.
3) You can adjust the transmission firmness/sloppiness with the vacuum activated transmission modulator. A very easy task.
it is located on the left side of the transmission. There is a plastic cover (about 2 1/2in diameter).remove carefully. Turn the adjustment counterclockwise for firmer shifts, clockwise for sloppier shifts. Only a few degrees at the time.