Hi I’ve got an older Volvo a40 truck, when it’s cold it works fine. But once it warms up the hydraulics on the bed start cavitating..... both up and down. And if you watch, the cylinders kinda go up at different speeds, one will go an inch then the other an inch then back to the first then the other. Except at regular speed. And like I said. It does the same thing going back down. The filters and oil have all been changed, and just a small amount of super fine sludge like metal. I believe the steering runs on the same system, and it doesn’t seem to have any issues.
I would shoot your bed lift cylinders with a temp gun and see if one side hotter than the other. it sounds like your piston seals are bypassing.