Hi Mike. Thanks for your feedback.If you can slow it down by applying force against the PTO shaft - than it's not a mechanical connection issue that's causing the problem - it has to be "gear drag" as mentioned earlier. There is no need to pull cover.
You could try a different oil (i.e. lighter viscosity or multi-weight) to reduce drag if this is an issue you want to correct
PS. Please don't try to grab any rotating object. I don't object to pushing a board up against the rotating shaft (even that can be dangerous), but don't grab the shaft. With gloves, a metal bur/splinter on the shaft could grab a glove and twist your arm.
When I place a bit of wood against it it does slow. But it's fighting it and goes back to the same speed when I release the bit of wood. It's not running around 540, but it's still pretty steady.
So if it were drag wouldn't it stop after I applied pressure to it, rather than start up again?
When I apply the clutch it stops (like it is supposed to). It's as though it is still in gear although slower.