Did the Transaxle just get rebuilt?
If the shifter forks aren't aligned in with the shift lever then your transaxle will give you these exact symptoms.
I was lucky enough to find this before I stabbed my ZF onto the motor.
It requires you to pop the back of the ZF (the cast cover, and the rear housing) to get in there and align the levers. It's like a 3 dimensional jigsaw puzzle.
Hopefully it is something simpler than what I describe.
Good luck
Rocky
P.S. I called Roy Butfoy (RBT) and talked with him when I had the same symptoms, and he told me this. I verified it was true on the second disassembly of my box.
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