..I replaced the knock sensor & it solved the stumble. During the time I had disconnected it I only got a cel once, strange. The car definitely when into limp mode, poor acceleration from no timing advance. I didn't need to remove the intake manifold to replace sensor. Now I see how much power I lost from a knock sensor degrading. A degraded knock sensor quietly robs performance.
..with this much power it's clear my cats are ok, not plugged.