Brakes Soft on 97 GMC pickup

[jmmmshowers]

Looking for ideas on what the problem is with my brakes. I have a 97 GMC pickup and sometimes it takes very little pedal pressure to stop and other times I have to push it to the floor. The lines have been bled and new pads and shoes were recently installed. The brake booster and MC have been replaced in the last 2 years. It seems like I'm loosing vacuum when it won't stop easily, but I can't find any leaks. The engine is a brand new stock 350. Any help would be appreciated.

 

[RLGL]

So, what happens when a vacuum gauge is placed in the system? Bad MC? Was it new or a re-man?

 

[Sabrewings]

Traveling to the floor doesn't indicate a lack of vacuum. If you lose vacuum it'll go down a little further, but mostly just firms up and takes more foot pressure for the same stop force.

I'd look at the bleeding. Was the ABS modulator properly bled with a scan tool? Poor man's way of doing this is inducing a skid to make the modulator cycle its valves and push the air out, then you can bleed normally and get it out of the lines.