Eli Mccurry

I'm having the same problem with a 01 gmc sierra 2wd it's got all 4 disc breaks wasnt having no trouble with them until I put new break pads all the way around and then notice a break caliper sticking so I buy a new caliper put it on and then after that I notice all 4 of my breaks holding. I have opened my bleaders and there is no pressure there so I go up to my master cylinder open the 2 lines on it to see my wheels will release and after opening them they still want release. So I then take it off the booster and still no difference I'm lost right now because I dont see how all 4 calipers went bad at once and i dont see all 4 break lines going bad at once. All I did was replaced the breaks and now I'm lost. Cause theres no fluid built up on the caliper nor theres no fluid built up at the master cylinder. Is it possible it can still be the master cylinder or the booster or the abs module? All the help I can get will be appreciated because I dont want to buy all new calipers along with a master cylinder booster and abs module so let me know your thoughts