If you shorten your top link it will tip the mower towards the tractor and should stop the pto shaft from rubbing. Can you get a picture from the back showing the actual mower ? Might be able to see why the grass is jamming up.
According to JD website the knives are cutting at 95mph. Hats off to you if you can mow that fastI have a JohnDeere 25A flail mower that I have been using. I noticed that the knives are rotating toward the back. So, that means that the faster I go with the tractor, the LESS efficient the knives are cutting. I guess they are running at ?30? miles an hour equivalent and if I drive 10 miles an hour instead of 5 miles an hour, the knives aren't cutting as well.
I could never find the number. Good to know that 5 miles an hour is not really going to make a difference. Other users NOT running the tractor at 540rpm makes way more difference.