Master cylinder or air PAC ?

[Ducelove]

I've had issues with my breaks since I bought the truck and just a few days ago the breaks where working great now I can't even get them to stay primed and always have to pump up the pedal what are some tell tale signs of a bad master cylinder or air PAC ?

 

[Boatcarpenter]

When you are looking for answers to your questions in the Technical Manuals provided free on this site, remember to spell BRAKES properly or you won't have much luck finding the information you need.
BC