1985 Buick Lesabre

I have an 85 Buick Lesabre that is jerking and running rough at speeds of 40mph and above. It seems sluggish like it is not getting power at any speed. The problem first started when I put new spark plugs and wires. It started running rough afterwards. I bought bad wires so got a new set and put on. It still did not fix it. Then the transmission fluid was low and got over filled and I removed the excess. I started losing fluid and the pan screws had became loose. I am not losing fluid anymore but now it is still running rough and speeds above 40mph or more it is jerking. If I am at a steady speed it does not jerk only when accelerating. I also just put on new distributor cap. Could it be the transmission or something else?