when driving & as i start approaching 40 mph the car begins to vibrate roughly.

What is your question?

first time this happened was today. outside temp was about 20 F. with icy, "greasy", snowy roads. The faster I drove the vibration would get faster too. I called it "chugging" because the vibration was a forward and back motion, not a side to side. I had a full tank of gas. Car has 39,000 odometer. I got off the expressway and drove to work on side streets so I could keep the speed under that 40mph threshold. (p.s.-may be Un-related but for the last year and a half the "low tire pressure light" comes on once every week and I put air into all the tires as specified on door jamb. ..wonder why they keep losing air?) (p.p.s.- occasionally when braking, the car will pull to the left...not all the time...just once in a while. weird!)