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riboyster you're better off running the tank nearer empty otherwise you could be allowing a greater mix % of the poor fuel, which it does sound like. However by a few re-fills I'd have expected that one bad batch should have been mixed enough to a better blend. Maybe a seasonal change or some left in storage?
Are the ambient temps increasing? Could be higher post charge temps as the Sprintex is susceptible to it. You do mention that you're running an aggressive tune....