It sounds like the transmission may be slipping. The transmission may just be low on fluid, or there could be some other problem. I would suggest that you take it to the dealership and have the problems diagnosed as soon as possible.
This problem will probably only get worse and you may find that the vehicle won't move at all eventually. It could just be something simple.
〉 Answered on Feb 27th, 2007 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines