John Deere D140 mower clutch

Hi all,
Hope someone can give me some Insight here. Last weekend, tractor ran fine. Wednesday I get it out, fire it up, pull the PTO switch, and can hear it clunking, but mower deck will not engage. Tested PTO switch, wire harness and seat switch with Ohm meter. All passed. Tested battery running and not running. Passed. Removed clutch assembly. Cleaned it out real good, including blowing it out with an air hose. Re-installed. Same thing. I can hear it clunk when I pull the PTO switch. But mower deck will not engage.
Went to John Deere, and spent $250 on a new clutch assembly. Made no difference. You can hear it clunk, but no mower action. I tried turning the pulley with key in off position, and PTO switch in off position. I could turn the pulley with a lot of effort. Then I tried putting k y in the On/Run position, and pulled the PTO switch to On position. I could turn the pulley rather easily.
I'm stumped.

Have you checked to see if the blades turn easily? Is the clutch pulley spinning, but not moving the belt?

All 3 blades turn easily by pulling the belt at the clutch pulley. I'll try taking the belt off, and put a mark on the pulley to see what it is doing when engine running, and PTO engaged. I think it is spinning, but not sure. Putting a mark on it with a marker will help these old eyes see for sure.

Is there a keyway on the shaft for the blade clutch/pulley that might have a sheared key in it?

Check and see if your clutch is the adjustable air gap style, and you may have to check to see that the gap is .012-.018 depending on model.
You should be able to removed the belt, turn the key on, dont start, and pull the pto knob. Watch the clutch move in and out, and snap into place. If it does not, then adjust or replace.