Kubota B1750 HST hydraulic problem

[Hmrhead]

I have a B1750 HST that us very slow to build hydraulic pressure after it has sat for a day or so. When I start it up, I can't raise the loader until I give it At least 2500 rpm and work the steering wheel back and forth several times. ( power steering) everything seems to get stronger the more the tractor is worked. I have checked and cleaned both hyd fluid screens and replaced filter and hyd fluid. Has anyone had a similar problem?

 

[jimmysisson]

Maybe a sludged up relief valve? Do you know the history of the tractor; fluid changes etc. any chance of freezing temps and a bit of moisture in the relief area?
My questions don't speak to why it improves as it warms up, except the last one, so hmmm.
Jim