We get this question every summer. The transmission doesn't know or care whether the a/c is on. The more the throttle is open, the lower the vacuum produced by the engine, and the harder the transmission shifts. That's how the car is designed - smooth shifts when you're just strokin' along, firm when hurrying.

With the a/c running, you gotta give the car more throttle to move down the road - the a/c is sucking up a bunch of the power produced by the engine. More throttle equals firmer shifts, as described above. If you want softer shifts, try accelerating more slowly

- JimY