Forget about those listed towing capacities, you're going to run out of payload capacity before you reach those larger towing capacities, especially if you load down the vehicle.
If it was me, I'd be aiming for a vehicle that had better gas mileage but I don't know the miles traveled. 4x4 SUV's have some of the worst MPG. Have you looked at what a Ford Ecoboost supercab and how it might work for you? If buying new, the newer Dodge with the Eco diesel may also offer what you need, better mileage unloaded and the ability to tow a fair sized trailer.
