1998 Chev C1500 5.7L Auto,With anti-lock brakes, NO CEL, SEL, or warning lights of any kind.163k mi. I recently replaced the rear brake line because the original one had holes rusted in it and leaking brake fliud. A spongy brake pedal was observed before this. The line was bled in the usual way, farthest from master cylinder first etc. I also performed a rear axle brake job and adjusted the shoes to as close to the drum without contact as possible. Drove the truck applying brakes forward and in reverse to adjust the usual old way.The front brake pads have been recently replaced and rotors turned.I still experience a spongy brake pedal and in a "panic brake " situation the brakes seem to be weak. Is there a test for a weak master cylinder? Am I bleeding the brakes properly? Do Anti-lock brakes require special bleeding?