Your PTO clutch gap may be getting excessive.

1. Agree with Mr Plum your air gap setting my well be off from the factory 0.20 setting . Alternately your pto switch may be going south a continuity test would verify . If gap and switch are within spec your electric pto clutch may have a internal short which can be intermittent and tough to verify .

also check condition of wires going to the clutch. Sometimes the tension spade on the packard 56 terminal fails. this is located inside the connector plug