You need to check the brake hoses for swelling under pressure (lose shape when brake is applied) but do not leak. Thier should be three brake hoses one on each front caliper and the third attaching the axle to the hard brake line on the body. I bring this up due to having the same problem your having on a repair of an older vehicle, I had put in all new hydraulics (calipers, pistons, master cylinder) as per customers request, I pressure bled them, no luck. In a panic I changed out the brake booster (at my cost), no luck. It was the stupid hoses swelling! I hope this helps you out.