CAT 315 cl hydraulic issues

we have a cat 315 cl intermintaley have no hydraulic power. machine can run for a couple of days and problem reoccurs. the machine will move slightly under what seems to be only pilot pump pressure. hydraulics load when activated and attempt to move but only have 500 psi. every possible wire and ground i could think of has been traced and found to have proper voltage. the problem has resolved its self now twice on its own. while testing pressures and voltages attempting to diagnose the issue the proportional reducing valve solenoid has been unplugged with the machine running when an audible change in the engine and pump sounds occurs and all functions return to normal. this is not entirely recreatable, just unplugging the proportional reducing valve solenoid while the machine is running does not resolve the problem. its not like the hydraulics are locked via the lever in the cab but more like the high pressure is not being generated every pressure test preformed at the pumps have checked normal but no high pressure to move and functions of the machine swing, travel, boom, or bucket. I am not a professional mechanic but i have purchased the shop manual and have spent days trying to dyspher the contents to no avail. Im wondering if anyone has had any similar problems and if there is a specific valve that engages the high pressure or if the relief valve could be stuck only allowing the 500 psi. we have only owned the machine for few months and are trying to fix it our selves before having to spend countless dollars for cat to diagnose it. if anyone could help it would be greatly appreciated.