Well it doesnt sound like your lifting ram has failed, it sounds like your latch seal has, so your latch wont release and you cannot build pressure to the ram to lift the cab. Like was mentioned earlier in this thread, disconnect the hose from the cab latch and cap it. I forget where exactly it is “Td“ off of the line to the ram, but a way to seal the line with what you have on the truck is to find that T, disconnect the leg to The latch and connect a line from a different circuit, say the Line to the bottom of the passenger side suspension compression cylinder, To that port on the T where the latch is normally connected. The suspension cylinder lines are also Td to go to the driver and passenger side cylinders. Those Ts are back Down below the air operated pump a foot or so and are fairly easy to get to(Just disconnected one the other day).
once you get the system sealed you need to manually release the cab latch. You can unscrew its piston/cylinder to allow you to manually release the latch mechanism. You will have to unscrew it to replace its seal anyway.
once the latch is released and system sealed, you should then be able to use the manual pump to pump up the cab. You can also pressurize the air system using a compressor by adding air at the front emergency glad-hand Which will fill the system tanks. Chock the wheels as this also releases the parking brake. Once the Air system is pressurized you can use the air operated hydraulic pump to raise/lower the cab...