Truth of the matter is that every single one of us that ventures into the forest to skid trees should have a full roll cage on their machines. I don't and did logging for a living . I cannot tell you how many times trees or broken limbs slapped the skidders. Perhaps it is the nature of a big cumbersome woods beast such as a skidder to be prone to bump into things but several hitches scumbling against the same tree during repeated turns on the same route can loosen things up top sometimes. To those of us with no protection, keep a wary eye up top on your skidding routes.
Artisan, I did the same thing to my tractor (JD 750) adding shims to the hydraulics and did not notice a huge difference. I should have used all five washers that came in the package instead of just the 4 I felt safer with. I pressured out to a little under 2300# with the 4 washers on a borrowed gage.