PC50UU-2E Hyd Problem

I am a beginner at track hoe work although I have owned this machine for 4 years and built a road and other simple jobs. I am retired and do not use this machine in a business, just on the acreage I have in Tenn.. My problem is after it warms up while using it, it starts to jerk back and forth when the boom is lowered or lifted. Also the travel jerks when I try to ease forward slowly. When grading I hit a rock and it stopped and jerked back and forth. At the time I didn't check to see if it was the left or the rt side only. I have a service manual on cd and have been studying to understand how it operates hydraulically. It has a 5 spool and 4 spool control valves. The 5 spool works the boom, the RH travel motor and bucket work off the same relief valve. The arm and LH travel motor work off a different relief valve. I have this at home now and want to get a pressure gauge to test the pressures. It has a plug on the hose fitting at the relief valve for the boom. I thought I would put a gauge at that fitting and see what the relief pressure is. According the the manual the best I can figure out is pump pressure is 210 kg/cm sq = 2987 psi according to chart. Should the relief valve relieve at this pressure? Any ideas and help would be appreciated. I busted a hose last month and loosing all my fluid, after replacing the hose I used John Deere HY-Gard 46-64 Hyd fluid since that is all I could get at the time. Is that ok for this machine? Ray