If you had a problem in the down safety valve, the fitting on the left side secondary cylinder you would not have a staging problem, rather the carriage would lower slowly. That valve is to provide a metered flow that prevents the mast from crashing down. Note that the down safety valve is not a velocity fuse,that will stop the carriage completely, so if you were to have a broken hose or line you would get a mess. But that is not the problem in your case.
But also check for binding in the carriage or mast rails.