Mike,
If the RPM drop started immediately after you replaced the stator, I would suspect the timing. You may not have to remove the engine again. All you need to remove is the magneto cover.
Another area might be prop pitch if you have an IVO prop. I love the ease of setting an IVO but they do have a tendency to change pitch when you remove and reinstall them. If it starts well, accelerates and runs well, your EGTs and cylinder head temps are the same as before, and your mag drop is normal, try adjusting the pitch.
Bill.
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