Why is my Motion platform unstable when lifting more that one player?

I scripted a moving platform and it works great going from "A" to "B" but only when one player is riding the lift. When I test the game with another player the lift is unstable and jerky. I used a body position and a body gyro to stable the platform. can you please help me figure out how to control the goals such as D, P and maxforse for the body position and body gyro. what do these values mean and what does changing them affect? Thank you for your help!