brake pedal hard to push down on 1996 Chevrolet S10

i have a 96 s-10, the brakes are hard to push down. almost seems as if something is holding back the pedal. just recently replaced the steel rear brake line. bled the lines and now having this problem. this problem occured little more than a week after lines were done. truck now only slows gradually not like it should.

sound like brake buster