3020 JD,
Welcome to TBN! You'll find a lot of information here.
You also started a thread about changing your hydraulic filter and cleaning your intake screen. You may have other reasons for doing that. However, I don't think that will help with this problem.
I'm not familiar with your machine nor the bigger tractors, but since no one else has posted, I'll offer what I can. Some of the larger (full size, maybe greater than 30 HP depending on how you measure it) tractors have "draft control" which (if I understood what I've read correctly) adjusts the level of the 3Pt hitch according to the drag the implement creates. So when a plow is digging too deep it creates a lot of drag, and the hitch is automatically raised to compensate. Your problem could be related to this if the draft adjustment is set incorrectly.
Try starting a new thread under the generic "Owning/Operating" group with a subject like "How to control 3PT depth". I think that will pull in more intelligent responses.