Hey guys im going to try and explain best I can.I did a Heater core job on son 2003 Liberty.Which im still not able to all the air out. But the problem started when After that I used the parking brake while I was working on it. And had to move the shifter to 4 lo to get center console out. Everything on this jeep seems to never been used anyway got stuck in for low manage to manual shift back to 2Hi. But brake pedal is Super hard now. They start off normal then as we drive they progressive get hard to press. I can let car sit for a while and its back to normal. but after alttile driving it gets hard and seems to me rear brake gets locked up. Took everything apart and removed parking brake. Also check valve and break boost seems to work fine with the foot pedal test. I tested vacuum from manifold its around 18hg. I can smell rear brakes heating up and when pedal gets hard to press the jeep dont want to move like almost 4000 RPM to get to 30mph. Ive tried eveything I can think of. Reinstalled the same pads and rotors and greased everything. It was **** dry. Also like I said if I let it sit awhile eveything works fine until you drive awhile.This was not a issuk before heatercore job. When I had to move the Shifter to 4lo and the e brake. Also I tested the 2Hi and it is in 2Hi.