1994/ Ford/ Thunderbird/ V6 3.8L/ Car shakes violently & idles low

Last week it was very hot in our area (100*F; record heat). I ran the a/c in my car a lot for the first time. A few days ago, for no good reason, the car started to shake violently when I drive it. Sometimes it snaps out of it and returns to normal, but then it goes back to idling at 400-600 and shaking violently. It sometimes makes a knocking sound when I put it in reverse as well. It still drives, but it feels like it has lost power and shakes bad at all speeds. I opened the hood, and I could visibly see the motor shaking and thrashing. All the fluids and lubrication has been well kept. Can you help me?