Chevy Transmission Problems HELP!!?

Ok so i brought a Chevrolet Lumina SS (2001 model) yesterday and there is already a problem! I was driving down the highway when all of a sudden the car stopped accelerating and just started revving? as if it had been put into neutral. when i pulled over and stopped the car it seemed to pull away fine then again it just kept revving no gear change and no power to the wheels. then when second finally kicked in (at about 6000 rpm) and i reduced speed when i tried to accelerate again the same thing happened! Its like it goes into neutral at every gear change? I really hope i don't have to change the transmission already! I know its a very vague explanationhe best i can do lol. Any help would be really appreciated.