Without seeing/hearing/driving the car, it's hard to diagnose, but assuming you have an ATX, it does sound like the tranny is starting to slip. Your first course of action is to change the fluid ASAP - I mean right NOW! You can do it yourself, drain out 4 quarts, replace with new. Drive for a day or so & do it again to get a substantial amount of fresh fluid in your system.
The fluid change should help if the tranny is not too far gone. If it doesn't help, effect repairs ASAP to prevent a total replacement/rebuild.
Perhaps some more CEGers can chime in with some ideas...