If that doesn't work, bypass the anti-lock valve above the rear axle. My brakes were spongy all the time, I had to replace a fuel tank strap, so I replaced the brake line to the back. When I did I by passed the valve, hooking the line direct to the axle hose. Of course I had to replace the hose and both wheel lines also (rust central). If you do this you have to unplug the brain box, or the lites will stay on. The best thing I ever did to the brakes, pedal is firm and the truck stops awesome. Thanks James!