It sure does seem like it is suffering from fuel starvation. I take it you have an inline fuel filter. I know that you checked it but you might put a piece of brass tubing in it's place for a test. Did you actually pull the carb screen out and hold it up to the light. I have found that sometimes a clear film can form on the screen making it look clean.

See if you can find a friend with a spare carb or one that could be pulled off of his engine just to see if the rpm would come back up.

I've been running the 10% ethanol blend for about 2 months with no problems, however, this might be your problem. The jury is still out.