Forgot to ask but is pump running all the time or when it shouldn't be and any lines warm?
I don't know enough about pressures and what should be where and when and where it goes to comment usefully. The lift cylinder packings fight each other between two cylinders and light pressure can allow the thing to work while full pressure can blow through a weak or bad spot in packer. A repack isn't bad but is time consuming and tricky solo as the cylinders are heavy and long. Just my two cents.
It sounds like it was doing it while running through both the SCV and the joy? I also was not able to apply enough down pressure to lift the front wheels at the time. That being said my 4020 and the 460 farmall...ones open the other is closed.