Tracking Or Steering Geometry
When the tracking was checked was it standard tracking gauges that were used or a computer geometry check system ?
The toe in or toe out can be on the right setting but the adjustment can be too much on one side. Look at the track rod ends and count the number of threads on both sides, they should be the same.
Is the steering wheel centred or off to one side ?
A computer check is the best bet as it will cover caster and camber as well as tracking.
If all this has been done swap the wheels back to front, I have had tyres cause pulling to one side.
There are many computerised tracking centres usually at a tyre depot.
Have you got your foot on the brake when it pulls to one side ?