I don't suppose you live in Virginia? It's tough for me to tune by description. I need to see and hear it to get it right.

I can tell you that sometimes the balance between the low speed needle and the idle screw can get way out of whack and it can be tough to get it right.

Another thing to try would be to see if someone can let you try a tank of their fuel. I know you said it was fresh but I have had so many people ask me to help tune their cars for them only to find an hour later that switching out their "fresh fuel" was all that was needed.

I assume you tried a new plug?

Hopefully Jamie has some more ideas. Don't give up on it. It is one awesome motor.