It is hard to diagnose without being there! We do not have any 800 series trucks, so I can relate from the multifuels, which I assume work in a similar manner. First, is the winch drive shaft turning at all times? On ours, the PTO drive shifts to neutral so it does not turn. Make sure that is happening. You do not want the shaft spinning while you are driving. If the PTO shift is disengaging, the PTO shaft is not turning, but the gears in the PTO box and associated gear in the transmission are constantly turning unless the clutch is depressed, stopping them. I suggest you pull the PTO gear box off the side of the transmission and check for damaged gear teeth. Another possible way to check it would be to back off the winch worm shaft brake tension until you can easily turn the shaft, have someone hold the clutch down with the PTO in gear, winch out of gear, transmission in neutral, engine not running, and turn the winch drive shaft by hand. You might feel an interrupted motion or click when a bad gear tooth meshes. If you keep track of how many turns you backed off the winch brake tension bolt on the side of the front cover, you can then easily return it to the original setting.
Regards Marti