Forum musta got slow after the holidays!
So your 150ish PSI no load is because that's the charge relief setting, that's the pressure it wants to keep the hydrostat drives pressurized at so it doesnt run out of fluid. The flow rate here is determined by system leakage in the hydro motor.
Your "load" pressure is the pressure required to lift the plow plus the hydro charge pressure.
The "dump" pressure is the implement relief valve setting, which does seem a little high to me.
The charge pump is fixed displacement, so it's output flow rate is determined by your RPM minus a little internal leakage. It's flow is split between the hydrostat circuit and the implements (including power steering). If your hydrostat is leaking internally a lot, that would slow down your implements. I would suspect actuating the steering would take away some flow, unless it's plumbed in series and tbh I'm not sure. Or your spool valve isnt opening all the way.
It could also be you need to rev up your engine
I found this to be very useful:
http://www.wfmfiles.com/download/Sau...evB_Jan93).pdf