2006 Pontiac Grand Prix Car seems to wander

I have been experiencing wabbles, shakes, general wandering, and a clunk noise with my 06 Grand Prix for over a year now. The shaking problem is noticed at low and high speeds, however seems to worse at speeds of 55mph and less. Additionally, the car wants to lean to the left anytime the road is the least bit uneven and is magnified when the breaks are applied. Alignment has been performed, balancing of tires has been performed, rotating of tires has been performed. The tires and wheels where purchased as a package about 12 months ago. The issues I speak of were noticed prior to the new tires and wheels.

Recently I brought the car in and described the issues to the mechanic. After checking the car over I was informed the intermediate shaft needed replacing, and the rack and pinion was leaking. These items were addressed along with an alignment, and tire rotation. The clunk noise is no longer an issue, the shake is not as bad, but the general wandering of the vehicle is the same. Any ideas? Thanks.