Do you have a compression gauge with you? Might be interesting to pull the plugs and spin it over and see what the cranking compression is. My guess is that it is super low.
x2. If it isn't the carb (worth putting a wideband on it for a pass just to check), my next guess is just a combination of E85, the altitude, 11:1 CR, aluminum heads and a roller cam. On E85 I would be surprised if you could get it to detonate at all. Might be worth advancing the cam a couple degrees to get cylinder pressure up and pick up midrange torque to pull through the converter more cleanly.
