1998 Trans Am Auto Trans Shifting problem

I recently purchased a 1998 TA with an automatic trans. Most of the time the transmission shifts fine. Sometimes when I get on it, the trans wants to slip between 1st and 2nd and also between 2nd and 3rd at high rpm's. Also, once in a blue moon, if I am pulling off from a stop at normal speeds, the trans shifts very very quickly through the gears and doesn't want to down shift when I press the pedal farther down. Does this sound like it could be computer related or a bad transmission? If it is computer related, where would I start looking to resolve this problem? Thanks for your help.