CAT 301.6C jerky boom cylinder movement

Hi.

I just got a hold of used CAT 301.6C mini hydraulic excavator. It has around 3000 hours. I tried it for a couple of hours yesterday and I noticed two things:
When operating boom cylinder especially with the arm fully extended and not loaded I frequently (but not always) experienced jerky cylinder movement. Sometimes so much that I had to stop and start movement of boom again. It seems (but I am not sure) that it happens more often when the machine is hot.
The other thing is track movement. If I want to move slow it starts to move jerky and I have to stop and start over. Unlike boom cylinder issues this happens always (no matter hot or cold). If I push the levers all the way (forward or reverse) it moves smooth but with top speed.
Otherwise I noticed no leaks and have just changed hydraulic oil and filter. The engine runs fine. The power is OK also under heavy load.
Can anyone point me in the right direction what would be the steps to try to solve this problem?

Thanks!

CAT 301.6C jerky boom cylinder movement