Try greasing well the two U-joints on the PTO drive shaft.
This assumes you've tested the assembly by disconnecting from the implement and slowly turning the PTO shaft--you can turn fast (540-rpm per your dashboard readout) but be certain the shaft is restrained from flopping around and getting away.
Confirm also you are not over-speeding the PTO by rev'ing the engine too fast.
Then lift the implement and check for bent broken chipped blades and / or foreign material wrapped around the blades / stump jumper / blade mounting bar.
If you replace one, plan to replace both blades for a matched set. Confirm also you have the correct blade for your model and direction of rotation. Check mounting bolts and tighten; confirm mounting bolt keyway is intact.
Don't crawl under the raised implement or attempt to work on it unless it is independently supported by chains and / or jack stands with the 3-point lift control in the full 'down' position.
Check also for gearbox on implement correctly lubricated with quality gear oil.
Please post back your experiences so we may all learn