Just replaced the master cylinder after 2 mechanics & myself tested the pedal and found that if we keep our foot on the pedal, it will eventually go to the floor.

Well, with a new master cylinder fitted, I have exactly the same problem. Push hard on the brake pedal and leave your foot on it, your foot eventually goes to the floor.

I've got new extended rubber brake lines as I have a 3" lift.

There's no loss of brake fluid.

Is this a Patrol 'thing'? I wouldn't have thought so.

Thanks for any help.