Hope you're doing well.

I'm reaching out because my team and I are having a significant, persistent issue with an H550HD forklift (equipped with a fork, GPI pipe stabilizer, and a PVG16 directional control valve), and we desperately need your expertise.

History of the Problem
The problem started 2-3 years ago when the hydraulic oil became contaminated. The tank was cleaned and the oil replaced. It recurred recently, which is when I got involved.

Repairs Completed So Far
Since then, after cleaning out the tank and changing all the hydraulic filters, we've replaced the hydraulic oil, carriage harness, all control valve seals, some actuators and PVEs for both the main and directional control valves, and re-kitted the main and tilt cylinders due to bad seals. The owners also replaced the hydraulic pump.

Current Situation & Symptoms
Despite these extensive repairs (re-kitted cylinders are fine, control valves serviced with new O-rings), we're still stuck. During testing:

The main lift and tilt arms are getting pressure.
However, there's no pressure or oil flow to the carriage (auxiliary) lines.
All PVEs on the main control valve show a green LED.
I haven't connected the carriage to the mast yet, as I wanted to confirm pressure to all channels first, though I did plug in the harness to avoid error codes.
Initially, the main lift and tilt arms moved quickly, but the carriage lines remained dead.
Then, the main lift and tilt arms began moving sluggishly, as if under strain, despite the auto-accelerate feature.
Eventually, all movement stopped.
My strong suspicion is the control valve, but given its cost, I'm hoping to get your insights before replacing it. Any advice or troubleshooting steps you could offer would be greatly appreciated.

Thanks,

Charles