Just a little update, with more to come. More to the story but short version is that I hoped that resolving the root cause of a pesky leak at the TC rear output would resolve my problem - needed to be addressed anyway, and in talking with my guy we could both see how it could POTENTIALLY have something to do with my bucking (wear on the bushing, so prop shaft a little loose)...but turns out to not have helped. Leak is gone, which is nice. Bucking still there.
But the more I think about the whole thing, the more I observe...I am back to suspecting the cats. And I've now identified a metallic clanging in that area, that seems like a smoking gun. Contacted Summit, and they're under warranty (bought April of last year), they're going to send a new unit and take the old, free of charge. I'm just paying to have installed. Have to wait until early November for delivery, so...that's the news. Thanks again everyone for following along.
But the more I think about the whole thing, the more I observe...I am back to suspecting the cats. And I've now identified a metallic clanging in that area, that seems like a smoking gun. Contacted Summit, and they're under warranty (bought April of last year), they're going to send a new unit and take the old, free of charge. I'm just paying to have installed. Have to wait until early November for delivery, so...that's the news. Thanks again everyone for following along.