If a good 4 wheel alignment machine shows normal factory specs and side to side comparison is close (withing specs as well), a frame shop also can't do anything more. A frame shop can straighten bent frame components not normally fixed by replacing bent parts after a major accident (severe damage to frame (subframe) but don't think they'll do more than anyone else if a 4 wheel alignment looks normal.

You can eliminate the tires as your cause by rotating both left wheels to the right side, both r wheels then to the left. Keep fronts in front, not x crossing them. If the car then pulls or drifts to the left (opposite) side, you'll know that you have a tire problem for sure. On the other hand, if nothing's then changed then it's not tires causing your problem.

You could also have another problem, your brakes could be dragging, like perhaps a caliper is sticking? Just a thought.