Hi!
Check for the suction pump filter,i had a similar problem once but all hidraulic functions were afected.

Regards!

it is possible (not likely) that a pump could do that but it would probably be caused by severe oil starvation causing cavitation. is the oil foamy, is the system noisy, is the lift circuit affected? if it is a pump problem it will affect all systems including steering to some degree. where are you connecting your guage. dead head the steering and see if the symptoms change.

I'm still baffled on this one. Took the relief vavle out and everything seems in order. Adjusting the valve doesn't increase pressure. It's about 1500 max up to half throttle then it drops off to 900 at full throttle. This control valve has 3 electric solenoids. One shuts down the hydraulics when energized, I guess for the SAS. One needs to be energized to allow the forks to lower. And one on the tilt section that works the tilt self leveling feature, that shuts off when using that feature and the button is pushed and the forks are level. They all seem to be working fine.
Could the pump cause this problem? I've never seen a gear pump with the problem of pressure drop when the rpms are increased.

the releif valve on that truck is a double stem valve, the first section does lift and the second does tilt and auxiliary functions.
you can adjust the small stem without changing lift pressure.