How can you tell if you need a new power brake booster? on 1995 Chevrolet Astro

4.3L V-6. Has new brakes rotors drums and cylinders...Does not leak. Anti-Lock light stays on and the brake pedal will get soft and hard? Thank you!!!

Asked by for the 1995 Chevrolet Astro
scan test for codes could be a bad wheel speed sensor or whoever did the brakes forgot to hook up sensor