Well - yes - if the engine revs like mad and the car won't go - then the trans is slipping. If the engine won't rev - even in 1st gear - then the problem is with the engine !! Remember with that auto trans - you can select each gear manually - just no clutch to worry about.
Sounds very much like the trans is indeed slipping....I fear the worst.
My only personal experience with an auto was my little Datsun 120Y. Great little car, till one day I put it into drive and it went nowhere at all, refused to budge an inch.