91 Integra Auto Tranny Help

I just got a 91 integra Auto 1.8l and i'm having problems with the transmission. first when the car is cold the it wont shift to 3rd gear. when the car warns up sometimes it slips. when it slips all i have to do is put it in Neutral shut the car off and turn it back on put it back on drive and it drives again for a little bit then i have to go through the same thing again... Can someone please help me with the problem soon as possible. thank you.:banghead: