Take a look at the position of the rod that moves the park paw.
This view is looking in on right side of tractor, between the Diff loc solenoid and the aux valve stack.
When in park the position, the pic with blue arrow shows position.
When lever is in neutral, high, low or reverse, pic with yellow arrow.
Blue- park engaged
Yellow- park disengaged
That triangle piece that rod hooks to may be stiff moving causing it to not fully flip over center and get completely out of park.
Lube all your linkages and levers in cab. First thing to do and check. Hope this he