auto gearboxs have an internal switch and if you lose a certain amount of transmisson oil then "slipping" ocurrs, if no leak, then you need to top-up with correct transmisson fluid, then start the car and keeping the brakes on, go though all the gears to settle the fluid thoughout the gearbox. if this does not work, then it needs checking out with auto transmisson techie, which ain't cheap. good luck.
billsp, October 2012
