Chainring is a new Salsa, not ramped or pinned. Pretty darned centered to the middle of the cassette. Straight teeth.

HillRider, I'd say the same thing. But, that chain rolls like butter on the derailler. I removed the chain to clean it. I'm using a connex master link just like on all of my 9 and 10 speed bikes over the last several years.

My thoughts are that the thick packing grease made the chain realively stiff and that the "less stiff" chain made the difference. But that can't be THE problem, just a symptom.