Problem need help

There is something wrong with my slk230...my car is auto..and it seems like today while i was driving down the highway..my car seems like it was adding more gas than what i am giving it with the pedal...let me try to give u a better exampl..say i am doing about 70mph and the rev is about mid 3,000 it seems lyke its pushing 3,800-4,000 so my car keeps juking bak and forth...then when i reached my home..i stopped the car and put it in neutral and it kept reving up and down from 500-1,300 and just kept repetition its self...if u kno a solution or kno what the problem..is please help me

Thanks