What's wrong with my car besides the obvious?

Hello. My car is a 2004 Mercury Grand Marquis
with 353,051 miles. I just replaced my ground wire.
My car idle hard on start up, but then calm down.
Now after about 5 minutes of warming up, the car
start shaking, more like rocking from side to side. I
do have to replace my intentional pulley, but there's
a ticking coming from the right side of the engine.
That ticking didn't start until I used the Lucas oil
stabilizer during my last oil change. I'm due for a
tune up also. My main problem is when I first start
the car up, the oil pressure hand starts off in
between the H and L, but after 5 minutes of the car
running, the hand drop all the way down and the
car start sputtering and then cuts off. What is
wrong and how can I fix it?