What compression are you running?

What speed have you had the fuelling tested to?

Has this been det checked or just AFR checked at these speeds? I ask, because although the AFR could be perfect, an engine can still det, so you HAVE To use det cans as well as AFR checking....

I personally think it is as a result of your high speed escapades with Doug and the possibility that your manifold gives higher flow to one cylinder .

If it is perfectly equal, then my other GUESS would be that it was cylinder pressures due to too high compression?

Sad for you, especially as you had just got transmission sorted .