It's always best to start a new thread. The original poster had a completely different problem from yours...
Have you checked the oil level in the rear differential section (rear end)??
Next thing to check is the PTO clutch system operating pressure. You should have a plug on the bottom of the pump. Clutch pressure should read 160-180 psi at a fast idle (~1000 rpm).
If the clutch system operating pressure is within limits, my guess is that the clutch pack is the problem.
To make fluid level checks: See attached photo. (photo and writeup compliments of Harry16)
On the right side of the transmission there is a small SQUARE-HEADED pipe plug for checking the tranny fluid level. White pencil in photo points to this plug. Filler cap is on the top of the transmission near the gearshift levers. Drain plug is underneath the transmission. Add oil (Ford 134D oil) till it comes out the fluid level check port.
Further back on the right side of the rear differential section, there is another small SQUARE-HEADED pipe plug for checking the rear differential center housing fluid level. Yellow pencil in photo points to this plug. Filler cap for the rear end is on top of the center housing, behind the seat. Drain plug is underneath the rear end. It may be under the draw bar, requiring you to remove a pin and slide it back to get to the drain plug. Add oil (Ford 134D oil) till it comes out of the fluid level check port.;