In my opinion:
I agree with the link not to install gable or power vents.
Are your soffit vents continuous?
Are your ridge vents continuous and NOT of the nail-over foam type? The ridge vents need to be the baffled type to allow proper air flow.
Are your bath and kitchen vents vented to the outside and NOT into the attic?
Is there a tree or other shade directly over the problem area? Perhaps you need the trim branches, etc.
To kill the mold, I would suggest a bleach solution and a garden sprayer.
Good Luck!
Dodgeman