Nissan Pathfinder Brake problem

You stated drum rears?I would guess they are properly adjusted?I've had a few similar issues with Asian cars and trucks that customers have thrown money at, and than asked for help.The low first than high hard second pump leads to a volume (not pressure) issue.The fact that you keep checking the level and its not changing eliminates leakage.Recently I had a mitsu come in with the exact issue. First, do you have any steering wheel pulsation when braking?warped rotors "widen the space required between the pads requiring more fluid to push the pistons in on first application.Second issue in the north east (thanks salted roads and ocean breeze here) is corrosion especially with Asian vehicles. I've had front pistons that wont "self adjust due to the inability to slide out through the seals, so the when the brakes are applied the seal rolls in its bore and when released acts like a spring and pull the piston back in to far ,again creating to large a gap between the pads and rotor and again requiring more fluid (pedal travel) on first push. I hope this helps.