Brakes lock up

So first off, I do not have a pathfinder. It is a 1986 (Non-hardbody) 720 4x4. I have changed everything in the system and I still get a pressure buildup while driving (in front driver). New caliper, software, and removed and cleaned all hard lines. Master cylinder is 2 years old so I will be replacing that again, but I don't think that is the problem as only the front driver is building pressure while driving and the passenger side is just fine. There is a single line for the front brakes that comes out of the master and then goes to a "T" block to split between the left and right. I have removed and cleaned/replaced everything from there on and I'm still getting pressure buildup.