If you are considering Jeep Grand Cherokees, watch out for their rated payload capacities. They are surprisingly low given their ruggedness. It is quite a bit lower than most 3-row crossovers. You will likely to hit the payload limit well before the tow limit.
I think the closest you are looking for is a F150 with EcoBoost. When empty and if your foot is light, then you get a pretty good fuel economy. And as others have mentioned above, your mileage will suck regardless of your vehicle when you tow. In fact, it has been shown that most vehicles, regardless of their size and engine, ends up returning similar MPG when the same trailers are pulled. Except Diesels, of course.
