This is not a direct answer to your specific question but I also have
a 99 Durango 5.9L and am located in Connecticut. The gas here for a
few years by law has contained at least 10% ethanol and my D runs just
fine on it. I cannot imagine that an additional 5% would make any
difference. I've seen no difference in either the mileage (stinks)
or the performance (great).
Hope this helps.
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