Need Brakes help ASAP

Ok so I plan on getting my 97 nissan back on the road this weekend after this winters stockfloor body drop. The only thing I have left to do is figure out the brakes. I reused all the factory brake lines, nothing has changed. everything was disconnected of course. Ive bleed all the air out of the lines and with the truck off, the pedal feels nice and firm. But as soon as I turn the truck on, the pedal gets very mushy and takes about 5 pushes to firm up, but if you let go and start over again, it goes right back to being mushy. I know its not air. Ive bleed that bitch like 8 times already and im pulling my hair out cause I really wanna be draggin rockers for memorial day weekend. Any help at all would be so greatly appreciated. Thanks guys

abs unit messed up maybe?

hey man same thing happened to me but my peddle stayes hard once u pump it up lol anyway i noticed that my master cylender was leaking slightly but enough to mess things up all fixed now gl and check it out