Brake bleeding problems

[cfranklin013]

I have run out of things to check . I have replaced my complete brake system on my truck ,now I cant get the brake pedal to pump up . I have gravity fed the brakes, fluid runs good through all for corners. I have benched my master cylnder three times ran 3 qts of fluid out of the whole system . The brake pedal will get stiff but will never pump up then when it sits for a few seconds it will be loose again . I have no leaks that I have found .should be dripping on floor after 3 qts of fluid . The details are 9" booster corvete style master front and rear disk new prop valve all new lines . Any help will be appreciated . Im over looking something .