well, i have 2000 silverado 1500 4x4. 120 000 miles. yeah, brake fluid is getting there, sorta slimy.
if you have ABS, ABS light will come up every time you start the engine, for about 5 seconds. also, ABS unit is right underneath the driver seat. best bet is to note VIN and call dealer. GM and Ford are mindbogglingly procreative in optioizing their cars.
anyhow. if pedal goes down to the metal, and nothing comes out of bleeding screws, you have no pressure in the lines. i ABSOLUTELY doubt all four lines got bent or plugged.
btw, keep in mind, Silverados are known for having mushy, soft brakes.
my bet is - one of the seals inside master cylinder is bad. or both. hence, it is not pumping up.
here's suggestion. remove bleeder screws, as of now, they are useless anyway. run compressed air to master, if no compressor - maybe find a buddy with surge tank and high pressure nozzle attached to it. disconnect brake lines from master, and blow them with compressed air. if they check out, remove master. if you just want to buy a refurbished one, it's your call. repair kits are sold everywhere, and it is very easy to refurbish yourself.
when done, bench bleed master. master bleeding kits are sold for pennies. reconnect brake lines, and reinstall bleeder screws. bleed system. have PLENTY of brake fluid on hand. we bled inlaw's work van not so long ago, it took quite a bit of fluid in.
i hope, you do not turn engine on to bleed. also, i have bled lost count how many times, never had any issues with pedal to the metal range. yes, you do have the right order.
if you do have ABS, then tough, you need to follow bleeding procedure for ABS systems.
Code:
http://www.aa1car.com/library/abs_bleeding.htm
i just checked with my repair manual. they do not caution from pedal going to the floor; if you have ABS, when you done with bleeding, ABS light should come up when you start the engine, and go away in about 10 seconds; if it stays, you screwed and ABS must be diagnosed with special tool. and no, they do not specify any special procedure for bleeding after master re-installation, for ABS. bench bleed/reinstall/bleed master when installed/reconnect lines/bleed lines.