I have a 2009 mud buddy hd 6000 and noticed that when I am in deeper water and set the trim higher it will go down on its own slowly. I suspect the trim pump or motor is going out but thought I would ask here for opinions.

I'd ask in the migratory bird section. You definitely have a pressure issue. Could be pump could be a line.

Do you have Thompson trim unit or a Mercury? Mudbuddy used Bear then Thompson trim units till 2009, after that most of them were Mercury units.
Based on what your saying its doing I assume its probably a Thompson. The internal bearings are rusted from water intrusion and will slowly go down under a load.

They are linear Actuators and are no longer used, they do not last long, I am on my third one granted mine is 11 years old with a lot of hours on it.

DO not try to find one on your own and use it, I went down that road and did not last a month, just buy a new one from Mudbuddy, they have a grease zero on them now to make them last longer.

If its a Mercury unit, there are up and down trim actuators that can be changed just like on an outboard.

PM for more information if you need it.