Brake help please....

[elks]

So I have a 1972 Chevy Blazer. It has been lifted running 36" tires. The brakes have always seemed a little weak. So this spring I decided it was time for new rotors, pads, drums etc. So I got all of it switched over. Got the system bled and had decent (not awesome) brakes in my inital test drive for about 4-5 good hard brakes. After the 4-5 test, the brakes were gone... Nothing. the pedal sits all the way to the floor, the lights stay on etc. There is no fluid leaking, the master is full and I even bled it before the line bleeding. I did it all in the right order etc.

Does the fact that there is no pedal mean my master cylinder went bad? It is not leaking, but I can't really even pump the brakes.

If it is a master cylinder, what up grades can I do that will makes the system better with out costing tons of money and forcing all sorts mods. Can I swap in a larger cylinder? Aftermarket upgrades? Or will a new master make all the difference. I have had the blazer for a little over 3 years, not sure how old the cylinder maybe....

I don't mind reading if you find a link.... I searched did not my situation per say.