I have a 96 Gmc 6.5 td k3500 4x4. When I bought it, it had a rotted rear brake line. Truck had been sitting as far as I know about 5 years. I replaced: brake lines, rubber brake hoses, wheels cylinders, shoes, calipers, pads. I bleed the system, also manually bleed the abs system after realizing I still had 0 brakes. Got ansy and installed a lift kit on it, went through the whole process again. Same thing. Engine off: pump brake pedal, builds pressure but never hard as a rock. Start engine: goes straight to the floor while applying brakes. Clean fluid. Power steering pump works as it should. Before I replace and rebuild the entire system, can anyone give me some advise and thoughts?