1983 320i, no power and other things

I just bought an 83 320i. Two days ago it was running fine. I started it this morning and went to drive it and it takes forever to gain any speed. when its in neutral the engine revs fine, but when in gear it just takes forever to gain any speed... I have an automatic... 3 forward speeds.... Is it the transmission? Maybe I need to put more fluid in? Also... Is it normal to be running high revs? On the freeway im going 70mph at 4Krpm's... Is this normal? someone please help...