at 60mph on a flat highway, when I let go of the wheel, car pulls off the lane after about 3 seconds. It is always to the left.

ruled out tire problems, front end misalignment, and brake dragging.


what are other possible rootcauses?

 

This happened to me when I first got my car and i brought it in to the dealer to get it fixed. Since our cars are FWD, torque steer is at fault. Also, make sure to get tire rotations when they are due.

 

Bent suspension or bent frame.

How is the rear wheel alignment?

Regarding the alignment-- alignment machines can also lose calibration and become inaccurate.