have installed power brakes 1 year ago. when my truck sits a couple of days, I have to pump them to get a pedal. I have bled them a number of times. This brings the pedal back up , until I let it set agian. My first thought was a bad master cylinder, I changed to a new one last week. Drove yesterday, same problem!! I have completly checked all lines and fittings, no leaks..Any ideas? thanks