If you can't get a more straight flame you either have a vacuum or draft problem. The vacuum problem could be thorny. Lots of possible causes. The draft problem, well, after all you've done the only thing I can think of is exhaust size. One other question: If I red ypu right the problem exists when the temp goes below 10f but nothing else is changed, including feed rate?
Well, I do try to leave it on a higher settings in the colder weather to keep the house warmer, but as of last year, yes, the problem occurs on level 3 at 5 degrees but not at 15 degrees.
The pictures posted reflect about 8 hours of burning at level 5. I'm not sure if the same thing would happen at level 3..havent tried.