Well it turns out I was very wrong on the gearing. The rear gear on the Wagoneer is a 3.92. That is probably a huge factor in sucking the fuel economy down. Mainly because, especially in my Durango, 8th gear is not tall enough for optimal highway cruising rpms. I think the same engine with a 3.09 gear like the 392 L cars have, would net me an additional 2mpg on my highway cruise in my Durango SRT. But, I still get right around 20mpg at normal highway speeds. Even can get almost 11mpg towing my camper, which is pretty impressive.