.050 shorter is lot for a spring in a relief valve.
Yes replace the spring. i think your on the right track.
For the guy with the IH a flow divider problem. please check the pressure at your hyd outlets and then check that with the recomended pressure.
If the outlet pressure is within 150 psi of recomended pressure then try and reseat the check ball or just replace the ball and spring and seat if the seat is replacable.
if the above doesnt help then Does your tractor have a dual pump. Its possible to have a problem on the power steering side of a dual pump.
If that doesnt get it, then check the relief valve in the steering spool valve.
Steering valves differ but normally there is a dump valve or return pressure valve in the steering system that can cause a low pressure problem/ lack of steering