I have a 1989 Cadillac brougham with 79,000 miles on it and when it gets heated up it acts funny cont.....?

it acts like it is goin into the gears real early and gets real jerky when you accelerate and decellerate the engine acts like it is bein under powered when i hit the gas it only happens every once in a while also it shakes and almost cuts off while ideling when this is happening can anyone help i am a car guy and this is baffling me