1995 Toyota Pickup brakes

Hi there, I had both calipers replaced and checking the brake fluids and flushing the lines because of braking problems. My mechanic suggested that I have two new tires and rotate and balance done to my truck. While having this done, the new place determined that I needed two new brake lines from Toyoto. The truck was pulling to the left when I brake hard. All this was done and the mechanic said it was fixed. We drove it back to the mechanic and he rotated and balanced the two back tires and flushed the brake line. Still pulled to the left hard. He changed the metal connector and reflushed the lines, drove the truck and told me it was fixed. I still cannot drive the truck without pulling into the left lane when I apply the brakes. They say all the joints, shoes etc. Look good. I need help please. I have spent 4 days without my vehicle. Thanks