No offense jerry g, my experience with fork lift trucks ( 22 years ) we have had little to no luck with used parts.

Sometimes you do get very lucky, but the majority of the time when you roll the dice you lose.

For the stress and aggravation try to go rebuilt or new.

Did a qualified tech reseal the tilt cylinders and install the valve control???

Now with that said I would get a pressure check valve tool to install in different locations to test pressure drop.

Check and double check the simple things first. You will be surprised