Clarification please. When the problem is present (tractor no go or go real slow) if you release the clutch with the tractor in gear and give it some throttle, does the RPM increase like you'd expect? If the RPM goes up under these conditions with a gear transmission, either the clutch is slipping or something has become disconnected in the drive train.
ANSWER: Yes, the rpm's do go up as expected.
I read that the clutch housing was dry: no water and no oil came out. This is good and bad. It means the possible problem with the easiest fix (clutch full of H2O, just drain and dry) isn't the case. But it also means that the a leaky seal probably isn't the problem either. I looked at the parts diagram (
OEM Parts) and the clutch is a 2-disk affair (separate PTO and drive clutches), relaitvely complex compared to the single automotive-style clutch on the DKs. I think it's possible thst something in that assembly has come lose or broken. The sudden occurrence of your problem leads me to believe that something mechanical (probably in the clutch stack) is your problem. In any case, I think it's dealer time.
ANSWER: I also think something has broken. Now that I think about it, I ran through a big rut in the field about 100 feet before it suddenly stopped. And I also feel that it's dealer time now. It seems like we've tried all the simple things now.
Also, you previously stated that it got better after you adjusted the clutch but later said it got better after several minutes of operation. Do you think the clutch adjustment actually changed anything or might that have been the second behavior that occurred after the adjustment by coincidence?