Vehicle pulls to the left when brake is applied

1993 GMC Suburban 2500 7.3L 4x4. One day, this truck just started pulling to the left when you apply the brakes. There hasn't been any recent maintenance on the brake system to cause this. I checked the pads and they are like new. I bled all for brakes just to be sure there wasn't air in there, but it's still pulling to the left. The Anti lock light has been coming on for a few seconds every once in a while, but never stays on. Could the anti lock brake manifold be causing this? I see that there is a special way to bleed the anti lock manifold, but I don't have the special tools for holding the valves open (J-39177). Any thoughts on where to look from here would be appreciated.