Spongy is one thing, but if pedal goes to floor, that's a big problem. You need to read CPP instructions again. It specifically states that you must remove all components from MC. Use short long strokes and tells what to plug off and where to attach enclosed bleeding kit and to make sure MC is off the truck and level. I think that is your problem. The first step in your "pinch hose" test is to plug the MC and test, if that gives hard pedal, proceed to release one clamp at a time until spongy. That is supposed to identify the circuit that is faulty. I think all that is a bad idea. If MC is bled and each wheel is bled and no leaks, it will not be spongy with good parts, correct fluid and proper valves. New wheel cylinders in rear? As last resort, check under the wheel cylinder boots for small leaks.
