Now there is some good info. I was indeed using a brand new KMC X10SL chain. I would use the Sram chain, but I'm running Praxis chainrings and they recommend against using a Sram chain. So my casette wants a Sram chain and my chainrings want a KMC chain. Oi!
Given that the 2011 RD runs fine with the KMC chain, what would cause this on the new RD? Is it the new pulleys?
i wonder what is the reason for parxis recomending against sram chains. i has a similar problem with my 2010 red rd with a yaban chain, but swapped to a dura ace 7900 and things became butter smooth.