1992 Chevy Astro severe pull to the left side

1992 Chevy Astro AWD mileage: 125,000. We have a severe pull to the left side when braking. We have checked the pads and rotors, changed the calipers, and new shocks. We jumped the ABS system and found that it needed a new micro-valve (costing $900) so instead of buying we wanted to make sure that was the problem and by-passed the ABS system by going from the master cylinder to the breaks. This still did not solve the problem of the very aggressive pull to the left when breaking. We have looked at the sway bar, looked ok, but we are not sure about the torsion bar that goes towards the rear of the vehicle. We are looking for ideas of what would cause this pulling to the left. While driving it, drive straight down the road with no noise. Once the brakes are applied, the vehicle will seem to straighten back up but by that time, you are in the opposite lane ready to be hit by an oncoming car.