Brake Issue

[Mattman2010]

My 1980 K10 is starting to have a brake issue. When you put your foot on the brake it is solid and when you let off the brake you have to push the pedal even farther down to get it to brake, but it is still solid not spongy like air in the lines. Also when you have the truck in gear and have your foot on the brake it will "bleed off" and the pedal goes farther to the floor. When it does this and you push your foot down with it it will hit solid.

So to me it doesn't seem like it needs the brake lines bled, and I am not sure how to test the booster or anything else on the system. What do you think the problem could be?

Matt