1998 Nissan Maxima Vibration at 50 mph and above

Hello, I have a vibration problem on my car. At slower speeds I notice no problems and than a wheezing sound as if air is escaping through a tiny hole somewhere. After a few miles of running, the oil lamp lights up. I had replaced the oil pressure switch (from Autozone, after-market). But when I accelerate the car in park or when I start moving the car, it turns off. It again comes back when I slow down to like 20 or 15 mph or parks my car. The vibration is also very exaggerated and noticeable when I am stopped somewhere in drive, and take my foot of the brake very little so the car moves forward by inches. I let go of the brake or apply brakes fully I dont notice it. I once happened to over fill the engine oil once to about 1 or 1.5 quarts more than required at night and next day there was a large oil spill under the car (I didnt spill it). I drove it around for 50 miles the next day on the highway. Any idea what is causing this? THanks a lot.