Might be worth investing some time & a few bucks to go over to the "small" dealer with the PTO Dyno & have them dyno it for you (post repair). Could the cable be mis-adjusted so that when you let go of the clutch it doesn't travel far enough to open the valve completely? I'd worry less about travel to disengage the pto (it just needs to be off) than making sure you had full pressure when engaged.